The late birthday effect in Western Australia

The "Late Birthday Effect" is a label given to the observation that students who fail to thrive in the early years of primary school are frequently those with late birthdays - e.g. in November and December. This effect is manifested in Western Australia where the rules for entering primary school result in late birthday students being developmentally less mature than the rest of their classmates. For how many years does this effect persist? Does it affect achievement in Senior Secondary School and, by implication, access to university?

An analysis of tertiary entrance scores for 17 year old Western Australian school leavers in 1992 and 1993 showed that for students who enter school at the normal time and who progress at the normal rate there was no evidence of lower achievement by late birthday students; however, there was a conspicuous shortfall in the number of late birthday students in this year group. A comparison with birth statistics showed that late birthday students are more likely to be aged 18 on leaving senior secondary school. They are also less likely to be university-bound than students with early birthdays.

A comparison of data from other Australian states confirmed the findings from Western Australia; namely, immature school starters are generally more likely to have their entry to school delayed or be made to repeat a year, but those who do progress at the normal rate suffer no disadvantage in access to university. Since the rules for starting school differ from state to state, this effect is attributed to developmental maturity rather than seasonal factors affecting innate intelligence. Since the removal of students from the "normal" cohort - by delaying school entry, making students repeat, or due to students leaving before the end of Year 12 - does not increase the mean tertiary entrance score of late birthday students who progress at the normal rate, it is concluded that such interventions are unrelated to academic potential.

[Key Words: Late birthday effect, Tertiary Entrance Score, school entry age.]

Introduction

This research was initiated by a question from the Ministerial Task Force on Voluntary Full-time Pre-primary Education and Related Matters, one of whose terms of reference was "...to consider the appropriate entry age for children entering a full-day program [of formal education], taking into account the situation in other states of Australia." The findings of this task force were subsequently published in a document informally referred to as the Scott Report (1993). This term of reference arose from one of the main concerns expressed about the full-time pre-primary policy operating during 1992: namely, that some children admitted to pre-primary centres were too young for a five days a week full-time education program. Currently in Western Australia parents may voluntarily send children to pre-primary centres at the beginning of the year in which their fifth birthday falls, i.e. shortly after their fourth birthday. In no other Australian state or territory is entry to pre-primary schooling possible so early; hence this state's particular concern about the late birthday effect.

The late birthday effect is a phenomenon well known to parents of children entering school. The extent of this effect has been reported variously: Kinard and Reinherz (1986) found that there were age group differences in achievement in the first year of schooling which disappeared in subsequent years; Sweetland and de Simone (1987) found that late birthday children in grades 1-4 performed at a significantly lower standard than their classmates; Mortimore et al (1988) found that 7 year old students with birthdays late in the school year did less well in reading, writing and mathematics, were twice as likely to have behavioural difficulties and were more likely to have a negative attitude to school than students born early in the school year; Bell and Daniels (1990) found that the effect could be found in students aged 11-15 taking science assessments.

Apart from a direct effect on academic achievement, the late birthday effect has been linked to other factors which would be expected to affect schooling: Diamond (1983), for instance, reported that late birthday students have a higher incidence of specific learning disabilities; and Jackson (1964) and Thompson (1971) reported that the late birthday effect is enhanced when internal assessment is used, since teachers tend to victimise the youngest members of the class. Routley and de Lemos (1993) describe strategies by parents to avoid the late birthday effect by delaying school entry until the next academic year and show that age on entry to school depends on sex and socioeconomic status.

In Western Australia the Education Act (1928) and its regulations make it compulsory for parents to cause their children to attend school at the start of the year in which their sixth birthday falls. This may or may not be subsequent to a period of pre-primary education. A small number of parents manage to negotiate a year's deferral of entry, but the majority of students enter according to policy. From then on, students in Western Australia normally march locked in step through one grade per year until they leave school. The only concession to developmentally appropriate practice is to advance or retard a very small number of students who are exceptionally conspicuous misfits.

Having access to data on senior secondary school achievement, the authors were asked to find out whether the late birthday effect persisted to the end of Year 12. This main question was broadened to ask:

• whether students with late birthdays may be expected to obtain the same Tertiary Entrance Score (TES) as those with early birthdays,
• whether students with late birthdays are as likely to stay in school to the end of Year 12 as students with early birthdays, and
• whether students with late birthdays are as likely to aspire to university places as those with early birthdays.

Method

In Western Australia, the variable Achievement was operationalised as the Tertiary Entrance Score (TES) calculated by the SEA. Subject to the restriction that at least one course must be taken from each of two categories - Humanities (not including English) and Science/Quantitative courses - the average of the best four scaled marks (maximum 100) from TES courses is compared with the average of the best five scaled marks. The higher of the two averages is multiplied by five and added to ten percent of the student's mark in the Australian Scaling Test, giving a possible maximum TES of 510.

SPSSPC Version 6.0 was used for ANOVA studies. Chi-square tests were carried out manually, using birth statistics as a basis for expected values.

Results

1. Data on seventeen year old Western Australian leavers with a valid TES who were in Year 12 for the first time in 1991 and 1992 were analysed by ANOVA. The effect of Age on Achievement of seventeen year olds was found to be non-significant when Age was operationalised as "thirds", i.e. four month periods with those in the first third born in January-April, the second third born in May-August and the third third born in September-December (see Table 1).

No two groups were found to be significantly different; however, it was noticed that this data set included far fewer students born in the last third of the year than in the other time periods.
2. The effect of Sex on Achievement was found to be significant but Sex and Age did not have a significant interaction effect on Achievement (see Table 2).

3. In case the use of four-month categories (thirds) is too coarse a measure of Age, Experiment (i) was repeated with a finer scale for Age. The effect of Age, operationalised as month of birth (MOB), on the Achievement of 17 year old Western Australian leavers was found to be non-significant (F = 1.44, df = 11,19804 , p = 0.146). No two Age groups were found to have significantly different mean TES when the Scheffe procedure was used to make multiple comparisons at the p=0.05 level. It can be seen in Table 3 that there is a considerable reduction in the number of students born in the last two months of the year.

4. Since the late birthday effect on 16 year old and 18 year old students was also of interest, a wider range of Year 12 leavers was considered. The subjects were aged 16-18 when they were in Year 12. Year 12 repeaters were excluded, but those who had been delayed at some other stage of schooling and those who had been accelerated were included. ANOVA was used to investigate the effect of Age, operationalised as 9 groups each covering birthdays in a four-month period (thirds) over three years, on Achievement. Age was found to have a significant effect on Achievement (F = 31x 57, df = 8,23935, p < 0.001). Table 4 shows which groups are significantly different at the p = 0.05 level.

The mean TES and the number of students in each age group are displayed in Figures 1 and 2 respectively.
5. The apparent deficit of late birthday students was investigated using data from seventeen year old leavers in 1992. These students were in Year 12 for the first time (i.e. repeaters were excluded). The number of seventeen year olds in Year 12 was compared with the number of persons born in each quarter of 1975. A chi-square test was performed using the data in Table 5 to test the hypothesis that students with late birthdays have just as good a chance of staying in step with the rest of their age cohort as any other student. It may be seen in Table 5 that the hypothesis may be rejected and that the major term contributing to a high value of chi-square is that of the late birthday students.

6. In order to find out if Sex was a factor in the previous result, seventeen year olds who left Year 12 in 1992 were categorised by Sex and two chi-square tests were carried out on females and males separately. The null hypothesis under test is that late birthday students (of each sex in turn) have as good a chance of progressing to Year 12 at the same rate as other students.

Figure 1: Variation of TES, by age group, Western Australia 1992-93

Figure 2: Distribution of ages of leavers with a TES, Western Australia 1992-93

Table 5: Observed and expected numbers of 17 year old Year 12 students, Western Australia 1992

For females, Table 6a shows a significant deficit was found in the number of students (Chi-square = 9.80, df = 3, p < 0.025). For males (Table 6b), the null hypothesis may be rejected with even more confidence (Chi-square = 16.51, df = 3, p < 0.005).
7. The cohort of students with birthdays in the last quarter of 1975 was examined to see whether a year's delay, at any stage in their education before Year 12, made them less likely to undertake studies which could lead to university admission. Only students reaching Year 12 for the first time were considered, and they were categorised as either 17 or 18 years old and as either university-bound or non-university-bound. The results are shown in Table 7.

Age on reaching Year 12 was found to have a significant effect on students' aspirations (Chi-square = 211.14, df = 1, p < .005). Students reaching Year 12 for the first time at the age of 18 are significantly less likely to be aiming for a university place than those who do so a year younger.
8. Students who completed Year 12 for the first time in 1992, aged 17, were examined to see if Age had an effect on their aspirations for higher education. They were categorised according to birth quarter and whether or not their course combination could lead to a TES (Table 8). For these 17 year old students, late birthday students were found to be as likely as others to be aiming for university (Chi-square = 0.88, df = 1, p > 0.10).

9. Students who reached Year 12 for the first time at the age of 18 were examined to see if their month of birth had an effect on their aspirations towards university.

No evidence was found to reject the hypothesis that late birthday 18 year olds are as likely to be university-bound as early birthday 18 year olds (Chi-square = .01, df = 1, p > 0.90) while attempting Year 12 for the first time.

Discussion

Students in the Western Australian system who progress "normally", i.e. starting Year 1 at the beginning of the year of their sixth birthday and advancing one grade every year, are more likely than their age-peers in the grade below to be enrolled in courses from which a TES can be calculated. (Students taking such a combination of courses will be described as "university-bound" even though possession of a TES is no guarantee of a place. We can be more definite about describing non-university-bound students because their course combinations can not possibly lead to a TES). It has been found in this study that students completing Year 12 for the first time at the age of 18 are less likely to be university-bound than those aged 17.

When 17 year old Year 12 students were examined, it was found that their month of birth had no effect on their TES nor on whether or not they appeared to be university-bound. Students with late birthdays may be expected to obtain just as high tertiary entrance scores as those with early birthdays. Students with late birthdays are as likely as those with early birthdays to be university-bound. However, amongst this cohort of 17 year old students the late birthday students appear to be significantly under-represented. This conclusion was reached by comparing the number born in each quarter with expected values derived from birth statistics. The shortfall of late birthday students in this age group is due to a deficit of both males and females.

It may be concluded that for students who start normally and make normal progress through school the late birthday effect has no effect on achievement nor on students' aspirations towards university. However, members of their age-cohort who reach the end of secondary school one year later are less likely to be university-bound and, if they are university-bound, may be expected to have lower tertiary entrance scores. For these 18 year old school leavers, those with late birthdays may be expected to have the same TES and university aspirations as those with early birthdays.

It is curious that 17 year old late birthday students may be expected to have as high a TES as students born in other months of the year. If, as a result of developmentally inappropriate practice in the early years of primary school, late birthday students fail to receive the same educational opportunities as other students, one might possibly expect these students to manifest lower achievement in Year 12. Alternatively, if they were not thriving in school, one might expect them to be more likely to leave school at the end of Year 10 or Year 11. In any case, the removal of the least able students from their year group ought to raise the average ability of those remaining. This is not found. It is as if the deficit in 17 year old late birthday students arises from removal of a random sample (as regards future academic achievement) from their cohort. Furthermore, students who reach the end of Year 12 one year later than the "normal" cohort as a result of either being made to repeat a year or of having their entry postponed by their parents are less likely to be university-bound and may expect to have a significantly lower TES.

Comparisons with other educational systems

In Western Australia, Queensland, the Australian Capital Territory, Tasmania and New South Wales it is possible to identify a group of students who, by virtue of their month of birth, will enter Year 1 of primary school as immature starters. The TES (or equivalent) and population of these immature starters were contrasted with those of a group of students with different birth months who reached Year 12 at the same time.

In Queensland those born from October to December are the immature starters. Their mean OP in 1993 was 12.75. Those born between April and September of the same year achieved a mean OP of about 13.1. (It should be noted that a low OP represents high achievement.) The nature of the OP scale makes it difficult to test the significance of this difference, but according to Allen (1994):

Those who are 17 in Year 12 achieve at about the same level regardless of birthday. However, those with late birthdays are more likely than those with early birthdays to be 18 in Year 12 and to be achieving less well despite being older.

In the ACT children born between January and April were identified as immature starters since they spend less time in kindergarten before entering primary school in step with those born in the second half of the previous year. The mean TER of the immature starters (63.82) was compared with that of students born between September and December of the previous year (62.66) and no significant difference was found (t = 0.99, p > 0.10). The number of immature starters was 644; the expected value based on birth statistics and the total population of this cohort of Year 12 students was 686. The deficit of immature starters in this cohort of school leavers was significant (chi-square = 5.12, p < 0.025).

In Tasmania children born between April and June may be identified as immature starters. The 1993 leavers included 306 of them, with a mean TES of 50.68. These students were compared with their classmates born between July and September in the previous year (the corresponding early birthday group) whose mean TES was 51.31. There was found to be no significant difference between the TES of these groups (t = 0.43, p > 0.25). The expected number of immature starters in this cohort was 348, and the actual number (306) was significantly smaller (chi-square = 11.81, p < 0.005).

In New South Wales immature starters may be identified as those born between January and April. Their mean TES in 1993 was 260. They were compared with other members of this cohort who were born in May and June of the previous year (mean TES = 266). Unfortunately, the data available did not include standard deviations so it can not be concluded whether this difference is significant. The numbers of students in these two groups were compared with birth statistics in a chi-square test which showed that populations did not differ significantly from expected values (chi-square = 2.84, p > 0.05).

In New Zealand the flexible entry system and the operation of a policy of developmentally appropriate practice make it impossible to identify any group of immature starters. The flexibility of their educational system results in a wide spread of ages amongst leavers (see Figure 3).

Table 11 summarises the findings above. The table shows that in nearly every case these immature starters have a significantly worse chance of progressing through formal schooling in step with others who enter Year 1 at the same time; they either have to repeat a year or finish school before reaching Year 12. However, in the case of New South Wales the achievement of Year 12 students who started and finished school in step is independent of birthday. Nor was there a shortfall in the number of immature starters. It is possible that this is related to a more flexible policy for advancing and delaying progress through Years 1 to 12.

The age distributions of university-bound Year 12 school leavers in several Australian states and New Zealand are shown in Figure 3. The vast differences in population between students in the various educational systems have been removed by normalising the frequency scales in order to see more clearly the shapes of the distributions. (It should be noted that for some states Age is shown in quarterly groupings and for others in four-month groupings - a result of the diverse ways in which data were supplied.) Despite the effects of truncating these distributions due to lack of data (e.g. the ACT distribution appears as if there may be a significant proportion of 19 year old Year 12 students), and despite extraneous effects such as migration into and out of the educational systems, Figure 3 allows us to see that Western Australian students finish Year 12 approximately 6 months younger than students from the ACT, Tasmania, New South Wales and New Zealand.

The vast majority of Western Australian students appear to stay firmly locked in step with their peers who start primary school at the same time.

Conclusion

In several other Australian states evidence was found to support the Western Australian findings that in Year 12:

1. late birthday students are as likely to achieve as highly as other students in the same class who started school at the same time;

2. late birthday students are more likely than other students to reach Year 12 one year later, achieve less well than those who made "normal" progress and be non-university-bound.

The fact that, in several states, the immature starters have the same average achievement as their peers suggests that the students who were held back were not lacking in academic potential; otherwise, their removal would raise the average achievement of this cohort. Their removal from the "normal" cohort is tantamount to removing a random sample, as far as future Year 12 achievement is concerned. An alternative hypothesis to account for this observation is that the loss of less able students (by making them repeat a year, or through their early departure from school) has exactly the same effect on the mean achievement of each age group, and leaves the mean TES of late birthday students in the "normal" cohort equal to that of other age groups. To believe this calls for acceptance of some remarkable coincidences in the data of several states.

Figure 3: Age distribution of Year 12 Leavers with a TES
Australian States and New Zealand 1992-1993
(Frequency scales normalised)

The authors of this paper are inclined to prefer the simpler conclusion that students who are made to repeat a year of school (and those for whom a decision was made to start school a year late) were selected for this treatment in a manner unrelated to future academic potential. This treatment is more likely to be applied to late birthday students (or immature starters in states other than Western Australia).

Doubtless, at the time it is decided on, there are good reasons for delaying the start of school or for making a student repeat a year - perhaps such decisions are based on students' behaviour. If so, one would expect a link between sex and making normal progress through the school system. A comparison, by sex, of birth statistics with the Year 12 population lends some support to this hypothesis.

Although there is no evidence for the late birthday effect operating at the level of senior secondary school its effects at an earlier stage of education may be permanent. Recent political debate in this state has focussed on a proposal which would entail, amongst other things, raising the school entry age by six months. This would simply transfer the late birthday effect to a different group of students. Although this might have some merit because the late birthday effect is probably attenuated by increasing the school starting age, it seems short-sighted to ignore the possibility of eliminating it by introducing more flexible entry to the early years of school.

Acknowledgments

References

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