Socioeconomic status (SES) is an important factor contributing to health inequality. This study aimed to investigate factors that predict junior school students' sports participation, identify the mechanisms underlying transmission of social resources and assess the mediating effects of classmate support and parental involvement on the relationship between parental SES and children's sports participation. 4829 males and 4536 females (mean age = 13.56 years, standard deviation = 0.686 years) participated in the study. Multivariate regression was adopted to analyze the determinants of junior school students' sports participation and multiple mediation analyses were used to analyze the hypothesized model. The results indicated that parental SES is significantly and directly correlated with junior school students' sports participation. In addition, parental SES has a significant indirect effect on sports participation through classmate support and parental involvement. Furthermore, the mediation effect of classmate support on the association between parental SES and sports participation is stronger than that of parental involvement. To promote and facilitate the participation of junior school students', strategies should be developed by government and social workers to strengthen classmate support and parental involvement.