The gift of time? School starting age and mental health
利用丹麦调查和登记数据，发现推迟一年入学显著降低7岁儿童的注意力缺陷/多动问题，尤其对女孩效果明显，该效应持续到11岁。
Using linked Danish survey and register data, we estimate the causal effect of age at kindergarten entry on mental health. Danish children are supposed to enter kindergarten in the calendar year in which they turn 6 years. In a "fuzzy" regression-discontinuity design based on this rule and exact dates of birth, we find that a 1-year delay in kindergarten entry dramatically reduces inattention/hyperactivity at age 7 (effect size = -0.73), a measure of self-regulation with strong negative links to student achievement. The effect is primarily identified for girls but persists at age 11.