Using an unanticipated policy reform in Mexico that shifted 4 months the cutoff date for elementary school eligibility in 2006 and information on academic performance of 15-year-old students from the Programme for International Student Assessment (PISA) 2018 survey, who entered first grade in 2006, this paper estimates the effects of starting first grade without having reached 6 years of age on middle-run academic performance. We found that entering school at a younger age increases the probability of having repeated at least one academic year by 7 percentage points and reduces academic performance (measured throughout PISA’s score points) between 6 and 10 score points in mathematics, reading and science (a Cohen’s d effect size between 0.06 and 0.10). We did not find evidence to claim that the effect of early entrance on academic performance is different for girls and boys or for urban and rural locations.

使用墨西哥一项出乎意料的政策改革，将2006年小学入学资格的截止日期转移了4个月，并通过2018年国际学生评估计划（PISA）调查获得了15岁学生的学习成绩信息，这些学生在2007年进入了一年级。 2006年，本文估计了未达到6岁的一年级对中级学习成绩的影响。我们发现，年轻时上学的可能性增加了至少重复一学年7个百分点的可能性，并且在数学，阅读和科学方面的成绩（在PISA的总分中衡量）在6到10分之间（科恩d效果大小介于0.06和0.10之间）。