Does it matter at what age a child starts school? Older children do better on tests, but is this merely because they are older and unrelated to the age at which they started school? Despite the dearth of convincing evidence, the popular press seems to suggest that there are benefits to “redshirting” (holding back) children in kindergarten. But is this the case? Are the short-run benefits in terms of better performance just that: short-run? And are there costs associated with finishing school and starting work later?

Starting-age effects in theory

There are a number of reasons why school starting age may have long-run effects on children’s outcomes, although the sign of this effect is theoretically ambiguous. The potential advantages of an early starting age could include the following:

  • Starting school younger means finishing school at a younger age, which implies more time for the individual to earn returns on their investment in education.
  • Starting school younger may also be advantageous to the extent that children learn more at school than at home (or be a disadvantage if the opposite holds true), which could affect their long-run trajectory.
  • Parental investment in their children may also depend on school starting age – parents may provide more help to children who are young for their grade level.

There are also potential disadvantages of an early starting age (and some of these could work in the opposite direction as well).

  • It is possible that children cannot learn as well in school earlier in their developmental life.
  • Social development may depend on a child’s age relative to that of his/her classmates; if being relatively older is advantageous, then it might be better to start later (and vice versa).
  • To the extent that older children have an advantage on exams in school (by mere virtue of the fact that they are older when they take the test and hence know more), they may do better in the long run.

Given these potentially offsetting effects, the true causal relationship becomes an empirical question.

Much research has shown a consistent pattern that children who start school later tend to score higher on in-school tests, even after accounting for the fact that school starting age can be a choice made by parents.1 However, a key limitation in the interpretation of these results is that children who start school later are also older when they take in-school tests. As a result, it could be that children who start school when they are older do better simply because they are older, not because they started school later.

An unintentional natural experiment by the Norwegian Army

To distinguish between the pure effect of age on tests and the effect of late-school starting, we rely on a natural experiment run unwittingly by the Norwegian army (Black et al., 2008). The administrative rule in Norway is that children must start school the year they turn seven. Children born on 31 December start school a year earlier than those born on 1 January – even though they are almost exactly the same age. This provides an exogenous separation between age and school-starting age. Our measure of performance is the military enrolment IQ test scores (when students are around age 18), which is taken by almost all children. This allows us to compare children of the same age but with different school starting ages.

To estimate the effect of age on IQ, we need children who have the same school starting age but different age at testing. In Norway, we have this, as there are cut-off dates for test-taking that are not the same as the cut-off dates for school starting age.

Results: Age matters but not school-starting age

We find evidence for a small positive effect of starting school younger on IQ scores measured at age 18. In contrast, we find evidence of much larger positive effects of age at test, and these results are very robust. The estimate implies that being one year older when taking the test increases the score by about one tenth of a standard deviation. On the other hand, accounting for age, starting school a year later reduces IQ scores by only about one fortieth of a standard deviation. Thus, it seems that school starting age has minimal impacts on test scores once one accounts for a person’s age when tested.

Beyond IQ

We also study the effects of school starting age on longer-term outcomes including educational attainment, early fertility, and adult earnings. Given the complications created by school leaving age rules in the United States, European data are attractive when studying education and earnings.2 Ultimately, adult earnings are a very important outcome, and we add to the literature the first study to track cohorts of men and women from ages 24 to 35 and analyse how the impacts of school starting age change with age.

For the purposes of studying earnings, we restrict attention to individuals aged between 24 and 35. In this group, about 94% of both men and women have positive earnings. For simplicity, assume that earnings depend on (1) labour supply and (2) the wage rate. At age 24, some Norwegians are still in full time education and performing little paid work. Thus, at these young ages, labour supply differences are particularly important. Because early starters tend to finish schooling a year earlier, this is a major reason they should have higher earnings at young ages. At older ages (late 20s and beyond), most individuals are working, so differences in wage rates are probably the dominant reason for earnings differences. Since wages depend on human capital, they depend on skills acquired in school and skills developed through work experience after schooling.

Results: starting late reduces earnings up to age 30

For men, our main finding is that higher school starting age leads to lower earnings until about age 30. Quantitatively, the initial negative effects are larger (about 10% at age 24) when all earners are included than when only full-time workers are included (about 5% effect at age 24). This is consistent with much of the earnings impact coming through differential labour supply, with older school starters working fewer hours at younger ages. The estimates for women in their 20s are generally similar to those for men.

After about age 30, the estimates for both men and women become close to zero and are almost always statistically insignificant. Given the large sample sizes, the estimates are quite precise and we can be confident that there is no large effect of school starting age on earnings in either direction once men or women are in their mid-30s.

Figure 1 presents a visual representation of the estimates (and the upper and lower confidence intervals) from the all-male workers specification. At age 24, the effect on male earnings is particularly large, being about 10%. However, this negative effect disappears relatively quickly and by age 32 is almost gone. Figure 2 provides the analogous picture for women.

Figure 1.

Figure 2.


Our findings reject the usual result in the literature that school-starting age matters. For men, there appear to be no long-term effects on education or earnings, and the effects on military test scores are very small when one allows for age-at-test effects. For women, there is little evidence of large impacts on educational attainment.

Overall, there are no strong reasons for parents to hold their children out of school or to time the births of their children to influence school starting age.


Angrist Joshua D. and Alan B. Krueger. 1991. “Does Compulsory Schooling Attendance Affect Schooling and Earnings?,” Quarterly Journal of Economics, 106, 979-1014.

Bedard, Kelly and Elizabeth Dhuey. 2006. “The Persistence of Early Childhood Maturity: International Evidence of Long-Run Age Effects.” The Quarterly Journal of Economics.

Black, Sandra E., Paul J. Devereux, and Kjell G. Salvanes. 2008. “Too Young to Leave the Nest? The Effects of School Starting Age,” NBER Working Paper #13969.

Dobkin, Carlos and Fernando Ferreira. 2007. “Do School Entry Laws Affect Educational Attainment and Labour Market Outcomes?” Working Paper.


1 There are many such studies including a cross-country study by Bedard and Dhuey (2006).

2 Studies using U.S. data have suffered from the fact that compulsory schooling laws specify minimum school leaving ages rather than grades so early starters have completed more education at the minimum dropout age. Therefore, historically, persons whose quarter of birth predicts starting early have on average higher schooling and higher earnings (Angrist and Krueger 1991). Dobkin and Ferreira (2007) find younger starters also obtain slightly higher education in more recent U.S. cohorts.

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