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British Journal of Educational Psychology (2013), 83, 651–663

© 2012 The British Psychological Society

www.wileyonlinelibrary.com

The relation between school entrance age and school achievement during primary schooling: Evidence from Croatian primary schools

Marija Sakic*, Josip Burusic and Toni Babarovic Institute of Social Sciences Ivo Pilar, Zagreb, Croatia

Background. Compulsory school entrance age and admission policies differ across

countries and educational systems, and there is a continuing debate on the question

whether and how the age at school entry affects various student outcomes.

Aims. This study explored the relation between school entrance age and school

achievement among students attending fourth (ages 10–11) and eighth (ages 14–15) grade of Croatian primary schools.

Sample. Participants were 44,479 fourth- and 43,338 eighth-grade students from all

Croatian primary schools. Students were divided into groups of younger and older school

entrants based on the difference between the year of birth and the year of school entry.

Methods. Differences in school achievement between students who were younger and

those who were older when they entered school in subjects covered by the curriculum

for respective grades were examined among fourth- and eighth-grade students. Two

achievement measures were used for each subject–objective test results obtained during a national examination and final school marks appointed by teachers.

Results. Among fourth-grade students, older school entrants on average performed

slightly better than the younger ones in all the subjects, irrespective of the achievement

measure used. However, these differences in achievement are very small, and the effect of

school entrance age onachievement isvery weak. In the eighth-grade sample, younger and

older school entrants did not differ in their achievement in the majority of subjects.

Conclusions. Students who are older when they enter school perform slightly better

than their older classmates in the lower grades of primary school, but these differences in

achievementareverysmallandareprobablynolongerpresentby theendofprimary schooling.

Compulsory school entrance age and admission policies differ across countries and

educational systems. In the majority of European countries, as well as in a substantial

number of countries in the world, compulsory school entrance age is 6, but it varies from 4

Portions of this data were presented as a poster at the European Conference on Educational Research, September 12–16, 2011, Berlin, Germany. *Correspondence should be addressed to Marija Sakic, Institute of Social Sciences Ivo Pilar, Marulicev trg 19, 10000 Zagreb, Croatia (e-mail: [email protected]).

DOI:10.1111/bjep.12000

651

to 7 (Bertram & Pascal, 2002; Sharp, 2002). In addition, in some countries, children can

enter school before the compulsory entrance age or delay entry, based on parental

requests, teacher recommendations or readiness testing conducted prior to school entry.

The question whether it is better for children to begin formal schooling at a younger or older age has been a subject of continuing debate among researchers and policy makers.

The debate is largely motivated by the potential effects of age at school entry on various

student outcomes, such as school achievement and different socio-emotional outcomes,

progress through the educational system, educational attainment, labour market

participation and lifetime benefits (e.g., Deming & Dynarsky, 2008; Dobkin & Ferreira,

2009; Kawaguchi, 2006; Lincove & Painter, 2006). In the majority of the educational

systems, children are eligible for school admission if they reach the compulsory school

entrance age by a certain cut-off date. Regardless to what entrance age is accepted and/or set as compulsory, this produces variability in children’s age at school entry, with possible

age differences between the oldest and the youngest students at school entry as great as

12 months (deCos, 1997; Lawlor, Clark, Ronalds & Leon, 2006).

Studies examining the effects of school entrance age and age position in a class on

various student outcomes have found differences in school achievement related to age,

with older students usually outperforming younger members of their class (Bedard &

Dhuey, 2006; Hutchinson & Sharp, 1999; Kalk, Langer & Searls, 1981; Sprietsma, 2007;

Stipek & Byler, 2001; Teltsch & Breznitz, 1988). This finding is consistent across studies conducted in various countries and educational systems, which differ with respect to

compulsory school entrance age, cut-off dates for school admission, school intake and

grade progression policies (e.g., Borg & Falzon, 1995; Fredriksson & Öckert, 2005;

Kawaguchi, 2009; Puhani & Weber, 2005; Sharp, 1995; Stipek & Byler, 2001; Verachtert,

De Fraine, Onghena & Ghesquière, 2010). Students who are younger in their class are also

more frequently diagnosed with specific learning disabilities (Martin, Foels, Clanton &

Moon, 2004), assessed to have special educational needs (Wallingford & Thompson Prout,

2000; Wilson,2000) and behavioural and emotional problems (Goodman, Gledhill& Ford, 2003; Polizzi, Martin & Dombrowski, 2007). Additionally, some studies have found

positive effects of being older at school entry on educational attainment and earnings

(Fredriksson & Öckert, 2005; Kawaguchi, 2009).

Different explanations of poorer achievement of younger students in comparison with

their older classmates have been put forward. These include maturational differences at

school entry or at the time the assessment of achievement is conducted, disadvantages of

younger students when compared to their older classmates in terms of abilities, skills and

behaviours, inappropriateness of formal curriculum for younger children and lowered teacher expectations for younger students when compared to their older classmates (see

Crawford, Dearden & Meghir, 2007 and Sharp, Hutchison & Whetton, 1994). In addition,

there are explanations that are content dependent and applicable only in some

educational systems. In the systems in which multiple annual intakes of students to

school are practised, younger children enter school last and receive less schooling than

their older classmates by the time the assessment of achievement is conducted. Thus,

possible explanations of the observed differences in achievement include differences in

the length of schooling. In systems in which, due to the month of the cut-off date, the youngest children at school entry are summer-born, while the oldest are autumn-born,

potential explanations include medical causes related to the season of birth.

However, it is important to note that not all studies have found differences in

achievement in favour of older students in class. For example, Kinard and Reinherz (1986)

compared school achievement in the third and fourth grades of primary school of six

652 Marija Sakic et al.

groups of students, formed based on their birth month in the calendar year of the school

entry. The effect of school entrance age on school performance was not significant when

cognitive abilities (i.e., information processing) were controlled.

The aim of this study was to explore the relation between school entrance age and school achievement during primary schooling. This was done by examining the

differences inachievementbetween students who wereyounger and those who were older

when they entered school in two cohorts of students attending fourth (ages 10–11) and eighth (ages 14–15) grade. The present study contributes to the existing body of evidence on the relation between school entrance age and school achievement in several ways.

Firstly, the differences in school achievement between students who were younger and

those who were older when they entered school were examined in two cohorts of students

attending the middle and final grade of primary school. This contributes to the evidence regarding the persistence of potential differences in achievement between younger and

older school entrants in primary school. The general conclusion based on data from

different studies is that the observed age-related differences in achievement favouring older

students are usually greater and ‘educationally significant’ in lower grades of primary

school, declining progressively in the higher grades (see Sharp, George, Sargent, O’Donnell

& Heron, 2009 and Stipek, 2002; for review). However, the age at which these differences

disappear varies across different studies. In some studies, they are no longer evident in the

third grade of primary school (Stipek & Byler, 2001), and in others, they are still present in the fifth and sixth grade (Borg & Falzon, 1995; Crosser, 1991), at the end of compulsory

education and in secondary school (Cobley, McKenna, Baker & Wattie, 2009; McPhillips &

Jordan-Black, 2009; Sharp, 1995; Sprietsma, 2007; Strom, 2004).

Secondly, in the Croatian educational system, in which the present study was

conducted, a single annual intake of students to school is practised, whereby children are

enrolled in the first grade if they turn 6 years by April 1 of the current calendar year.

Children enter school in September, when the school year starts. Thus, the majority of

children are between 6 and 7 years of age when they begin schooling. Assuming, they were not accelerated nor retained in grades, all of the students in the class are exposed to

the same length of schooling at the time of testing, so there is no confounding of school

entrance age and length of schooling effects.

Thirdly, in the present study, the differences in achievement between the younger

and older school entrants were observed across different subjects, to examine their

consistency. In some studies, older students outperform the younger ones across subjects

(e.g., Borg & Falzon, 1995; Kalk et al., 1981; Sharp et al., 1994; Teltsch & Breznitz, 1988).

On the other hand, Cobley et al. (2009) found differences in achievement between younger and older students in mathematics, science and physical education, but not in

English language among students aged 11 through 14. In addition, the progress of younger

and older students in the lower grades of primary school may differ across subjects, with

older students making a somewhat more rapid progress in mathematics, but not in reading

(Tymms, Merrell & Henderson, 2000).

Next, to further examine the consistency of age differences in achievement, two

measures of achievement in the observed curriculum subjects were used in the study,

namely objective test results and final school marks appointed by teachers. Older students usually outperform the younger ones irrespective of whether school achievement is

measured by average grades (Lien, Tambs, Oppedal, Heyerdahl & Bjertness, 2005) or by

achievementtests(e.g.,Baer,1958;Bedard&Dhuey,2006;Borg&Falzon,1995;Kawaguchi,

2009). However, one possible explanation of the observed age effects on achievement is

insufficient differentiation of younger and older students by their teachers when assessing

School entrance age and achievement 653

theirperformance.Ithasbeensuggestedthatteachersmayunintentionallyconsideryounger

children immature and underestimate their performance in comparison with older children

and that these lowered expectations may result in their poorer performance (Sharp et al.,

1994). As marks appointed by teachers are more susceptible to such biases, it is possible that differences between younger and older students are more salient when school achievement

is measured by school marks than when it is measured by objective tests.

Finally, there are some potential moderators of the effects of age at school entry on school

achievement, such as gender and socioeconomic status. Being among younger students in the

class may have stronger negative effects for boys than for girls (Crosser, 1991; McEwan &

Shapiro, 2008). Starting school later may have stronger positive effects for children from higher

incomefamilies,becausetheyhavemoreopportunitiesthanchildrenfromlow-incomefamilies

to accumulate important skills before they enter school (Elder & Lubotsky, 2009). Hence, to examine the stability of the effects of school entrance age on school achievement, we tested

whether the effects differ for boys and girls and for children of parents with different levels of

education, which served as an indicator of the family’s socioeconomic status.

Method

Participants

The participants in the study were students attending the fourth (ages 10–11) and eighth (ages 14–15) grade in all of the 844 primary schools in Croatia. Only those students who followed the regular school programme and were not accelerated nor retained in grades as

they started schooling were selected in the final samples. There were 44,479 students in

the fourth-grade sample and 43,338 students in the eighth-grade sample.

For the purposes of this study, based on the differences between the year of birth and

the year of school entry, two subsamples were created within both samples of students. These subsamples were labelled as the ‘younger’ and the ‘older’ group at school entry.

Among fourth graders, there were 9,536 students in the ‘younger’ and 34,943 students in

the ‘older’ group. In the eighth-grade sample, 9,730 students were qualified as the

‘younger’ group and 33,608 students were in the ‘older’ group at school entry. The

number of students in each subsample varied across the analyses, due to missing data for

some students on some of the measures used in the study. The national cut-off date for

school admission is April 1, and children are enrolled in the first grade if they turn 6 years

by this date. However, children begin schooling in September, when the school year starts. Thus, in both samples of students, the majority of ‘younger’ students could be

between 6; 5 and 6; 8 (years; months) and the majority of ‘older’ students could be

between 6; 9 and 7; 4 at the time they begin schooling. Some rare exceptions are possible

if, for some reason, children were allowed to enrol in school before they turned 6 years or

if they were advised to delay entry.

Measures School achievement in the majority of subjects covered by the fourth- and eighth-grade

curriculum was measured. In the fourth grade, achievement was measured in Croatian

language, English language (as a foreign language), Mathematics and Nature and society. 1

In the eighth grade, achievement was measured in Croatian language, English language (as

a foreign language), Physics, Chemistry, Biology, Geography and History.

1 The content of this subject largely corresponds to that covered in Science.

654 Marija Sakic et al.

Two measures of school achievement were used. The first measure was the students’

results in the objective tests assessing learning outcomes in respective curriculum subjects.

The ‘paper and pencil’ tests consisted of questions examining the students’ knowledge and

competencies in these subjects at the end of two stages in Croatian primary schooling, namely in the middle and final grade of primary school. The raw results on the tests were

transformed and expressed as percentage of points achieved on each test, ranging from 0%

to 100%. All the tests showed a clear single-factor structure, with almost all the items highly

saturated by the first principal component, as well as good reliability, with Cronbach alphas

ranging from .64 to .89 in the fourth-grade sample, and from .64 to .87 in the eighth-grade

sample, and as such they were used in the Croatian national examination (Babarovic,

Burusic & Sakic, 2009; Burusic, Babarovic & Sakic, 2008, 2009).

The secondachievement measure was thefinal school marks from respective curriculum subjects. The school marks are appointed by teachers and are based on the continuous

assessment of student coursework and homework, their participation in the classroom, and

their performance on various assignments and examinations during the school year. In the

Croatianeducationalsystem,finalschoolmarksforeachsubjectrangefrom1(inadequate)to

5(excellent).Thecorrelationsbetweenschoolmarks andobjectivetest resultsvarybetween

.53 and .62 in the fourth-grade sample and between .40 and .68 in the eighth-grade sample.

The mother’s and father’s education, which served as an indicator of family’s

socioeconomic status, was operationalized as a four-level categorical variable, with categories corresponding to possible levels of completed education in the Croatian

educational system (1 – primary school, 2 – secondary school, 3 – college, 4 – university).

Procedure

Data used in the study were collected as part of a national examination in Croatian primary

schools, during which students completed objective tests assessing their achievement in

the majority of the subjects covered by the curriculum for respective grades. Parental

consentwas obtained for studentparticipation inthe testing,and anonymitywas ensured in all phases of testing and scoring. All fourth- and eighth-grade students who followed the

regular school programme and were present in their schools on testing days participated in

the examination. The testing of students was carried out simultaneously in all the schools

during two consecutive days. Students were tested in classrooms in their schools, in groups

of up to 18 students. Testing and scoring was conducted by trained teachers, following

predefined and standardized procedure, and under the supervision of the national

examination centre. All fourth-grade students completed the tests in all the examined

curriculum subjects. Among the eighth graders, approximately half of the students completed the tests in Croatian language, Physics, Chemistry and Biology, while the other

half completed tests in English language, Geography and History. The allocation of students

into these two groups was done prior to testing by a random sampling procedure.

Data on students’ gender, year of birth, final school marks and parental education

were collected from the Croatian digital national database of all primary schools and

students (e-matica) and verified in communication with each school’s administration.

Results

To examine the differences in school achievement at two points during primary schooling

(i.e., in the fourth and eighth grade) between students who were younger and those who were older when they entered school, a series of one-way analyses of variance was

School entrance age and achievement 655

performed. The analyses were conducted separately for objective test results and final

school marks in respective curriculum subjects, as two types of achievement measures

considered in the study. The results of these analyses in the sample of fourth graders are

shown in Table 1. Among fourth graders, significant differences in achievement between younger and

older school entrants were observed in all curriculum subjects (Table 1). Students who

were older when they entered school outperformed on average those who were younger

at school entry across subjects, irrespective of whether achievement was measured by

objective tests or by school marks. However, values of Cohen’s d range from .02 to .07,

indicating that the observed differences in achievement between younger and older

school entrants are very small. Further, in the achievement in the objective test in English

language, the difference between younger and older school entrants was not significant. The same approach was used to examine the differences in achievement between

younger and older school entrants in the final grade of primary school. The outcomes of

the series of one-way analyses of variance in the sample of eighth-grade students are

presented in Table 2.

Among eighth-grade students, differences in achievement between younger and older

school entrants were not significant in the majority of the subjects (Table 2). Significant

differences in achievement were found in English language and Chemistry, when

achievement was measured by objective tests, and in Biology as well, when school marks were used as measures of achievement. However, contrary to the general trend observed

in the fourth-grade sample, younger school entrants on average outperformed the older

ones in these subjects. The effect sizes were again very small, with Cohen’s d ranging from

0 to .12. Moreover, in both samples of students, the values of eta-squared indicate that the

school entrance age explains less than 1% of the variance in school achievement in

different subjects. This can be considered as a very small or even negligible effect of school

entrance age on school achievement.

Additionally, we tested whether the effects of school entrance age on school achievement depend on student’s gender and parental education. Firstly, we conducted a

series of two-way analyses of variance with school entrance age and gender as factors and

measures of school achievement in each curriculum subject as dependent variables,

where we were primarily interested in the possible interaction effects. Analyses were

Table 1. The comparison of school achievement in different curriculum subjects between students who

were younger and older when they entered school (fourth-grade students)

Subject

Younger students

(born in 1998)

Older students

(born in 1997)

F p g2 Cohen’s dN M SD N M SD

Objective tests

Croatian language 9,440 56.63 18.87 34,613 57.63 19.15 20.05 <.001 .000 −.05 English language 8,309 57.58 24.96 30,413 58.17 25.25 3.57 .059 .000 −.02 Mathematics 9,435 52.06 23.80 34,568 53.41 24.50 22.86 <.001 .001 −.06 Nature and society 9,435 60.20 21.85 34,569 61.77 21.89 37.87 <.001 .001 −.07 Final school marks

Croatian language 9,522 4.15 0.87 34,895 4.19 0.88 19.94 <.001 .000 −.05 English language 9,517 4.25 0.93 34,888 4.27 0.93 6.39 .011 .000 −.02 Mathematics 9,526 4.04 0.95 34,904 4.10 0.96 27.31 <.001 .001 −.06 Nature and society 9,526 4.16 0.90 34,905 4.21 0.90 22.82 <.001 .001 −.06

656 Marija Sakic et al.

conducted separately for both types of achievement measures, and for fourth- and eighth-

grade samples. Among the 22 observed interaction effects, only one was statistically

significant ( p < .05), indicating that the observed effects of age at school entry on school achievement are the same for girls and for boys.

Finally, we tested for possible interaction effects of school entrance age and parental

educational level, which served as an indicator of family’s socioeconomic status, on

school achievement. We conducted a series of two-way analyses of variance with school

entrance age and parental education as factors, and two types of achievement measures in

each curriculum subject as dependent variables. The analyses were performed separately

for the mother’s and the father’s education, in both samples of students. Among the 44

observed school entrance age–parental education interaction effects, again only one was statistically significant (p < .05). This could indicate that school entrance age effects on school achievement are similar among students whose parents have different levels of

education.

Discussion

The results of this study show that school entrance age is weakly related to school

achievement in the lower grades of primary school, and its effects are no longer evident at

the end of primary schooling. Among fourth-grade students, those who were older when

they entered school on average outperformed those who were younger at school entry.

This difference in achievement is very small but consistent across curriculum subjects,

irrespective of whether school achievement is measured by objective tests or by school

marks appointed by teachers. On the other hand, in the eighth-grade sample, the

differences in achievement between younger and older school entrants are not significant in the majority of the subjects – both when achievement is measured by objective tests

Table 2. The comparison of school achievement in different curriculum subjects between students who

were younger and older when they entered school (eight-grade students)

Subject

Younger students

(born in 1994)

Older students

(born in 1993)

F p g2 Cohen’s dN M SD N M SD

Objective tests

Croatian language 4,713 46.05 17.39 16,211 45.58 17.63 2.63 .105 .000 .03

English language 3,788 61.06 24.62 12,795 58.09 25.44 40.49 <.001 .002 .12 Physics 4,750 55.50 21.12 16,704 54.84 21.30 3.57 .059 .000 .03

Chemistry 4,750 36.54 17.32 16,704 35.95 17.34 4.25 .039 .000 .03

Biology 4,750 42.54 18.32 16,704 42.31 18.38 0.60 .439 .000 .01

Geography 4,740 42.96 17.43 15,979 42.89 17.98 0.07 .795 .000 .00

History 4,740 50.18 16.95 15,979 49.79 17.39 1.89 .169 .000 .02

Final school marks

Croatian language 9,713 3.57 1.08 33,573 3.55 1.09 2.20 .138 .000 .02

English language 9,712 3.65 1.14 33,575 3.59 1.15 23.68 <.001 .001 .05 Physics 9,713 3.46 1.11 33,575 3.44 1.11 3.35 .067 .000 .02

Chemistry 9,713 3.49 1.12 33,576 3.45 1.12 10.62 .001 .000 .04

Biology 9,713 3.71 1.08 33,577 3.68 1.09 7.91 .005 .000 .03

Geography 9,712 3.71 1.09 33,572 3.69 1.10 3.15 .076 .000 .02

History 9,713 3.68 1.12 33,574 3.66 1.13 1.61 .205 .000 .02

School entrance age and achievement 657

and by school marks. When significant differences are found, students who were younger

when they entered school performed, on average, better than those who were older at

school entry.

It has been suggested that younger students in a year group may not be developmen- tally ready to begin schooling and to follow the requirements of formal curriculum and

that they are generally less mature than older students, which may lead to stress and failure

in school setting (Gledhill, Ford & Goodman, 2002; Kinard & Reinherz, 1986; Sharp et al.,

1994). For example, differences in brain maturation can be related to differences in

functions important for successful performance in school. These include functions

mediated by the frontal lobes, such as planning, verbal fluency and inhibition, which

develop intensively in the period from 5 to 8 years of age (Romine & Reynolds, 2005). It is

likewise possible that younger children may be at a disadvantage when compared to their older classmates with respect to cognitive maturity, but also with respect to physical

characteristics and skills, as well as social skills, which can lead to lowered self-esteem,

emotional and motivational difficulties and consequently poorer school performance

(Martin et al., 2004; Morrison, Griffith & Alberts, 1997). Additionally, formal curriculum

and teaching methods practised in lower grades may be aimed at and better suited for

older students, making it difficult for younger children to meet the necessary require-

ments (Sharp et al., 2009). Our results show that in the lower grades of primary school

students who were older when they entered school on average have a slightly better achievement than those who were younger when they entered school. Although these

differences are systematically observed across the curriculum subjects and achievement

measures, it is important to note that they are generally too small to be considered

educationally significant. That is, the effect sizes range from 0.02 to 0.07. Hence, the

results of this study indicate that the differences in achievement between younger and

older school entrants are negligible at the time they reach the fourth grade of primary

school.

Furthermore, among eighth-grade students the differences in achievement between younger and older school entrants are not significant in the majority of subjects,

indicating that any initial differences are completely lost by the end of the primary

schooling. This is consistent with studies that have shown that older students

outperform younger ones in the lower grades of primary school but that these

differences in achievement become smaller as children advance through grades and are

eventually no longer present. For example, Oshima and Domaleski (2006) examined the

differences in achievement between younger and older students in reading and

mathematics. They used a cross-sectional design and examined these differences among students from kindergarten through eighth grade. Effect sizes were used as indicators of

differences. Their results showed that the difference in achievement was largest in

kindergarten, declined rapidly up to third grade, remained relatively stable between

third and fifth grade and approached zero in the middle school years. Bedard and Dhuey

(2006) used data from Trends in International Mathematics and Science Study (TIMSS) to

examine the relative age effects in different countries and educational systems. Their

results showed that the difference in scores on nationally standardized tests between the

youngest and the oldest students is 4–12 percentiles in the fourth grade (9 years) and 2–9 percentiles in the eighth grade (14 years). It has been suggested that this may indicate that maturational differences that exert significant effects on achievement in

younger years become less important as children age (e.g., Baer, 1958) or that younger

children actually progress more and catch up with their older classmates by the end of

primary school (Stipek, 2002).

658 Marija Sakic et al.

An alternative explanation for almost equal performance of younger and older school

entrants in the sample of eighth graders in our study is based on teachers’ expectations

and classroom practices. In the Croatian educational system, in the first four grades ‘class

teaching’ is practised, and students have a single class teacher who teaches almost all the subjects. In the higher grades ‘subject teaching’ is introduced, and students have multiple

teachers who are experts in certain subjects. Hence, children change teachers at the

beginning of the fifth grade. If in the course of the first 4 years of schooling teachers have

learned to expect less from younger students in comparison with their older classmates

and by this contributed to their poorer performance, transition to higher grades provides a

‘fresh start’ for younger students (Hutchinson & Sharp, 1999). New teachers are not

burdened by the expectations formed during the early years of schooling, so younger

students are given a new opportunity to prove themselves, performing equally as their older peers by the end of primary school.

It is important to note that foreign language learning possibly presents a special case:

our results show that in the fourth-grade English language is the only subject in which

older school entrants did not perform significantly better than the younger ones, as

measured by objective tests, while among eighth graders, younger school entrants

significantly outperformed the older ones. English language is the only subject in which

the observed differences in average achievement were slightly more pronounced. These

findings are interesting in the context of the existing debates regarding the benefits of early learning of foreign languages (e.g., Marinova-Todd, Marshall & Snow, 2000).

Finally, our results suggest that the observed effects of school entrance age on school

achievement are independent of gender and of parental education level, as an important

indicator of family’s socioeconomic status. Although some studies show that gender and

socioeconomic status may moderate the effects of school entrance age on achievement

(Cascio & Schanzenbach, 2007; Elder & Lubotsky, 2009; McEwan & Shapiro, 2008); in the

present study, these effects were similar among boys and girls, as well as among students

from different socioeconomic backgrounds. Therearesomeimportantaspectsofthepresentstudythatneedtobeconsidered.They

aremainlyrelatedtotheallocationofstudentsintoyoungerandolderschoolentrantsbased

on their year of birth. As the data on exact birth dates of the students were not available, it

was not possible to group the students according to their birth month to examine the age-

relateddifferencesinachievementinmoredetail.Perhaps,adifferentpatternofdifferences

inachievementwouldbeobservediftheyoungestandtheoldeststudentsfromeachcohort

were compared. The division of students based on the year of birth also resulted in uneven

numberofstudentsintheyoungerandoldergroup–theyoungergrouprepresentschildren born in January, February and March, and the older group students born from April to

Decemberinthepreviousyear.Duetothis,itwasalsonotpossibletoexaminethepotential

season of birth effects. Additionally, in the context of contemporary debates regarding the

potentialbenefitsof‘redshirting’,thatis,thetendencyofparentstointentionallypostpone

their children’s entrance to school to give them additional time to mature (Katz, 2000), it

wouldbe usefulto compare the achievement of students who entered school ontime with

those who entered school earlier or delayed entry with respect to the compulsory school

entrance age. Such a comparison would be possible if exact birthdates were available. Furthermore, a cross-sectional design was used in the study, and it is possible that the

observed differences in achievement between younger and older school entrants are a

result of circumstances specific for respective cohorts of students. In this study, the

achievement of younger and older school entrants was compared in the fourth and eighth

grade. The differences in achievement between these two groups were very small in the

School entrance age and achievement 659

fourth grade, but it would be useful to examine whether they are greater in the first few

grades of primary school. Longitudinal studies that would test the differences in

achievement as students progress through grades are needed to examine whether they

aremorepronouncedatthebeginning ofprimaryschooling andat whatpoint they decline ordisappear.Finally,inourstudy,itwasimpossibletoseparatetheeffectsofageatthetime

oftestingfromtheeffectsofschoolentryage,astheyarecompletelycollinear.International

studies comparing achievement of students from countries with different compulsory

school entry ages are useful to separate these effects.

The findings of this study could have important implications for the educational policy

and classroom practices. It should be borne in mind that in this study the grouping of

students in the younger and older school entrants was based on the year of birth. The

comparison of such broadly defined age groups showed that the effects of school entrance age on student achievement are rather weak. The differences in achievement between

younger and older school entrants are negligible in the fourth grade, and they are no

longer evident at the end of primary schooling. In Croatia, April 1 is used as the cut-off date

for enrolment of children in the first grade. Thus, the majority of children are between the

ages six and seven, and even older than 7 years, at the time they begin schooling in

September. Policy implications of school entrance age studies are usually focused either

on the effectiveness of rising the school entrance age to eliminate any potential

differences between younger and older students or on the interventions at the level of curriculum and classroom practices that would reduce the effects of these differences on

student outcomes. In the educational systems in which the admission policy is based on

cut-off dates, the effectiveness of rising school entrance age to eliminate these differences

is questionable. There will always be younger and older students in the class, regardless of

what entrance age is set as compulsory. Based on the results of our study, it is possible that

the effects of school entrance age on achievement are not pronounced if the majority of

children are beyond the age of six at the time they begin formal schooling. Hence, setting

the compulsory school entrance age at six and using the April 1 as the cut-off date for enrolment in a system in which the school year starts in September appears to be an

effective policy in minimizing the effect of school entrance age on achievement. On the

other hand, it is often suggested that the differences in achievement between younger and

older school entrants can be minimized by adapting the curriculum in the lower grades of

primary school to be better suited for younger children and by modifying teachers’

expectations and daily classroom practices. Teachers may have an important role in

minimizing the effects of possible differences between younger and older students in

abilities, skills and behaviours on student achievement (Daniels, Shorrocks-Taylor & Redfern, 2000; Gledhill et al., 2002). This can be accomplished if teachers develop

awareness of these differences and their potential effects and adapt their teaching

approaches and methods, as well as their expectations and grading process, to take these

differences into account. As previously described, in the Croatian educational system,

teaching is organized differently in the lower and higher grades of primary school. Hence,

it is possible that these processes are already at work, and teachers manage to successfully

deal with differences between younger and older school entrants even in the lower grades

of primary school.

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Received 30 November 2011; revised version received 3 September 2012

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