Table S2.

Variable means across test time

Variable	All	Test hour
		8	9	10	11	12	13
Full sample
Test uncertainty	0.26	0.26	0.27	0.26	0.28	0.26	0.26
School day	179.89	180.10	180.02	178.81	180.49	180.83	179.80
Child birth weight (g)	3,298	3,307	3,304	3,300	3,303	3,282	3,272
Parents’ years of schooling	14.24	14.26	14.18	14.21	14.25	14.30	14.33
Household income, 1,000 DKK	386.17	384.64	379.79	386.07	382.60	396.16	396.96
Household income percentile	57.05	57.14	56.32	56.98	56.77	57.91	58.16
Nonwestern origin	0.09	0.08	0.09	0.09	0.08	0.09	0.10
Female	0.49	0.49	0.48	0.49	0.49	0.49	0.49
Spring child	0.50	0.50	0.49	0.49	0.50	0.50	0.50
Missing birth weight data	0.06	0.06	0.06	0.06	0.06	0.06	0.06
Missing education data	0.03	0.03	0.03	0.03	0.02	0.02	0.01
Observations	2,034,964	400,139	424,868	528,764	259,649	295,032	126,512
Subsample of schools included in the break data sample
Test uncertainty	0.24	0.24	0.22	0.25	0.27	0.24	0.25
School day	179.65	179.18	179.57	180.18	179.61	179.86	178.93
Child birth weight (g)	3,305	3,302	3,303	3,303	3,321	3,295	3,323
Parents’ years of schooling	14.29	14.26	14.17	14.30	14.35	14.38	14.40
Household income, 1,000 DKK	389.37	392.55	376.89	393.87	385.21	397.78	390.23
Household income percentile	57.25	57.43	56.11	57.42	57.06	58.10	58.18
Nonwestern origin	0.08	0.08	0.08	0.09	0.06	0.08	0.08
Female	0.49	0.50	0.49	0.49	0.49	0.49	0.48
Spring child	0.50	0.49	0.50	0.49	0.49	0.50	0.51
Missing birth weight data	0.06	0.06	0.06	0.06	0.05	0.06	0.05
Missing education data	0.03	0.03	0.03	0.03	0.02	0.02	0.01
Observations	121,709	25,561	24,025	31,198	17,039	16,995	6,891

The table shows simple averages for subsamples across test hours. Test uncertainty is the estimated uncertainty for the test result (only available for years 2011–2013). This variable measures how precisely the individual test score was estimated by the computer. (The uncertainty comes from the fact that the test can be more or less accurate to measure the student performance. Each question contributes to the precision of the test, reducing uncertainty. That is, the test is adaptive, and the computer tries to calculate the individuals level. For instance, if the student reaches a level where every time he/she gets a harder question, he/she answers wrong, but every time he/she gets an easier question, he/she answers right, there will be very low uncertainty on test score.) Income is adjusted to the 2010 price level and adjusted for household size using the square root approach. Spring child is a child born in the period January–June of the year being considered. Because the school starting age cutoff is January 1, these children have the highest expected school starting age. The variable called school days refers to the number of days from the start of the school year to the test day, not counting weekends. Parents’ years of schooling is the years of schooling completed by the mother or father (the highest value).