The drivers of month-of-birth differences in children's cognitive and non-cognitive skills

Abstract

Previous research has found that children who are born later in the academic year have lower educational attainment, on average, than children who are born earlier in the year, especially at younger ages; much less is known about the mechanisms that drive this inequality. The paper uses two complementary identification strategies to estimate an upper bound of the effect of age at test by using rich data from two UK birth cohorts. We find that differences in the age at which cognitive skills are tested accounts for the vast majority of the difference in these outcomes between children who are born at different times of the year, whereas the combined effect of the other factors (age of starting school, length of schooling and relative age) is close to zero. This suggests that applying an age adjustment to national achievement test scores may be an appropriate policy response to overcome the penalty that is associated with being born later in the academic year. Age at test does not, however, explain all of the difference in children's view of their own scholastic competence. Age adjusting national achievement test scores may help to overcome differences in ability beliefs between children who are born at different times of the year, but our results suggest that additional policy responses may be required.

Keywords: Age at test; Age of starting school; Month of birth; Non-cognitive skills.

Fig 1

McCrary density test: a window of 30 days on either side of the discontinuity is applied, with a bandwidth of 1; both discontinuities (across cohorts) have been pooled to increase sample sizes; a common sample is imposed; the McCrary density test was implemented in Stata by using the user-written command that is available here: http://emlab.berkeley.edu/∼jmccrary/DCdensity/

Fig 2

Overlap of age at MCS test: the sample includes only those living in local authorities that operated a single point of admission in the academic year in which the children started school; the key refers to the child's month of birth

Fig 3

Overlap of month of MCS interview: the sample includes only those living in local authorities that operated a single point of admission in the academic year in which the children started school; the key refers to the child's month of birth

Fig 4

Discontinuity in KS 1 scores: a window of 30 days on either side of the discontinuity is applied: both discontinuities (across cohorts) have been pooled to increase sample sizes; the model is as specified in Section Methodology and identifying assumptions, omitting background characteristics; a common sample is imposed (●, average attainment for pupils born a certain distance from the discontinuity (in days))

Fig 5

Discontinuity in WISC (IQ) standardized score (see the caption for Fig.4)

Fig 6

Difference in British ability scores at age 7 years, when measured at the same age or same point in time (the sample includes only those living in local authorities that operated a single point of admission in the academic year that the children started school; both sets of estimates account for a variety of individual and family background characteristics): , differences, on average, between those born in August and those born in other months of the year, accounting for age at test to mimic the case when children are tested at around the same age; , differences controlling for date of interview, thus mimicking the results of a test taken at the same point in time; , , 95% confidence interval around the estimates

Fig 7

Discontinuity in scholastic competence (reported by ALSPAC member) (see the caption for Fig.4)

Fig 8

Discontinuity in whether the child likes school very much (see the caption for Fig.4)

Fig 9

Discontinuity in locus of control (reported by ALSPAC cohort) (see the caption for Fig.4): the scale of locus of control moves from more internal to more external (less belief that they can control the events that affect them)

Fig 10

Discontinuity in global self-worth (reported by ALSPAC cohort member)