一个显而易见的现象就是：国内家长喜欢让自己小孩早点学习（不能说100%，但是比例很高）。
今天有了一片热乎乎的美国方面的研究：看美国学生提前一年进入代数学习是否有影响。

在谈这篇论文之前，我们谈一下咱国家的情况。
从现在风行的小学奥数来看，这到底能起什么样的作用？仁者见仁智者见智，但是一个客观的现实是：很多不适合学习奥数的小学生被迫牺牲课余时间来学习这个高度选拔性的课程。

美国高中之前的听说读写训练虽然远远高于国内同龄人，但是数学训练强度远小于国内。因此这篇论文的研究十分有意义：
Algebra for 8th Graders: Evidence on its Effects from 10 North Carolina Districts

This paper examines the effects of policies that increase the number of students who take the first course in algebra in 8th grade, rather than waiting until 9th grade. Extending previous research that focused on the Charlotte-Mecklenberg school system, we use data for the 10 largest districts in North Carolina. We identify the effects of accelerating the timetable for taking algebra by using data on multiple cohorts grouped by decile of prior achievement and exploiting the fact that policy-induced shifts in the timing of algebra occur at different times in different districts to different deciles of students. The expanded data make it possible to examine heterogeneity across students in the effect of taking algebra early.We find negative effects among students in the bottom 60% of the prior achievement distribution. In addition, we find other sources of heterogeneity in effects.




这篇论文的模型很简单，有兴趣的可以看一下