Organized extracurricular activities (EAs) are prevalent among Chinese preschoolers, yet their role in children's development is poorly understood. This study investigated the relations between EA participation and Chinese preschoolers' school readiness (N = 343; M[subscript age] = 55.14 months) among a predominantly middle-class sample. EA breadth had positive linear relations with children's early math and social skills, while attendance intensity demonstrated nonlinear associations, partially supporting the overscheduling hypothesis. EA breadth had stronger associations with early reading and math skills among lower socioeconomic status children, as well as greater benefits for math skills in children with less exposure to home learning activities, indicating a compensatory role of EAs. The findings highlight the interplay between EA and family contexts in relation to child development.