利用中国教育追踪调查（CEPS2013）数据，运用双变量Probit模型，基于参与时间异质性视角，分析初中生学业成绩与校外辅导班参与行为之间的关系，针对不同学生群体进行了分样本讨论，并进行了稳健性检验。研究表明：在“周一到周五校外辅导班参与”的群体中，学生学业成绩与校外辅导班参与负相关，即学业成绩越好，参与辅导班概率越小；在“周末校外辅导班参与”的群体中，随着学业成绩的提高，学生校外辅导班的参与概率经历了一个先上升后下降的“倒U型”趋势，平均而言，当语数外文化课总分为236分时，学生参加校外辅导班的可能性最高。“周一到周五校外辅导班参与”的群体中，学业成绩与校外辅导班参与之间的负相关关系在城市学生和七年级学生中更明显；在“周末校外辅导班参与”的群体中，学业成绩与校外辅导班参与概率之间的“倒U型”关系在农村学生和毕业班学生中更显著，城市学生学业成绩越好，参与校外辅导的可能性越高，存在“成绩越好，补课越疯狂”的现象。

Based on the perspective of participation time heterogeneity, this paper uses the China Education Panel Survey (CEPS2013) data to analyze the relationship between academic achievement and the choice of students' tutoring behavior via the Bivariate Probit model. With the endogenous treatment, this paper conducts a sample discussion on different students’ groups and conducts a robustness test. The results show that: From Monday to Friday, students’ academic achievement is negatively correlated with the participation of tutoring, that is, the higher the academic performance, the lower the probability of participating in tutoring classes is; At the weekend, with the improvement of students' academic achievement, the participation probability of tutoring experiences an “inverted U-shaped” trend of rising first and then decreasing. On average, when the total grades of classes is 236, students’ possibility of tutoring reaches the maximum. From Monday to Friday, the negative correlation between academic performance and participation in out-of-school tutoring classes is more pronounced among urban students and seventh graders. On weekends, the “inverted U” relationship between academic performance and the probability of participation in out-of-school tutoring classes is more pronounced among rural students and graduating students; the better the academic performance of urban students, the higher the likelihood of participating in out-of-school tutoring is and there is a phenomenon of “the higher the grades, the more crazy the participation of tutoring is”.

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