The Chinese education system is characterized as highly meritocratic and examination-oriented. Scores in high-stakes public standardized examinations mainly determine upward educational transitions. Private tutoring classes (PTCs) are a typical measure to boost students' academic achievement. Mental health is also assumed to affect one's behaviors and educational outcomes, playing a key role in the stratification process. However, few studies discuss (1) the bidirectional relationship between PTC attendance and emotional well-being, and (2) the role of academic achievement in determining PTC attendance and moderating the relationship between the two variables. This study fills these gaps by analyzing the 2013-14 and 2014-15 waves of data from the China Educational Panel Survey. Using a cross-lagged model, the author only finds a positive association between prior emotional well-being and later PTC attendance. Moreover, the positive association between students' prior academic achievement and their later PTC attendance suggests that PTCs tend to serve higher-performing students. Examining the heterogeneity of the bidirectional relationship in terms of academic achievement, the author finds that only low-achievers follow a similar pattern as shown in the full sample model. This study will enrich the understanding on how mental health together with PTCs attendance contributes to the educational stratification process.