Kindergarten Entrance Age and Children's Achievement: Impacts of State Policies, Family Background, and Peers
研究发现幼儿园入学年龄与学业成绩的正相关主要源于入学前的技能积累，而非年龄大带来的学习能力优势；该效应在富裕家庭儿童中更明显，且年长同伴能提高成绩但增加留级和ADHD诊断概率。
We present evidence that the positive relationship between kindergarten entrance age and school achievement primarily reflects skill accumulation prior to kindergarten, rather than a heightened ability to learn in school among older children. The association between achievement test scores and entrance age appears during the first months of kindergarten, declines sharply in subsequent years, and is especially pronounced among children from upper-income families, a group likely to have accumulated the most skills prior to school entry. Finally, having older classmates boosts a child's test scores but increases the probability of grade repetition and diagnoses of learning disabilities such as ADHD.