Since 2001, the Chinese government had passed a series of policies known as "the two primary responsibilities" to allow the rural migrant children to attend urban public schools. However, what the migrant children actually experienced in and after negotiating access to these schools deserves serious attention from educators, scholars and policymakers. Based on prolonged ethnographic fieldwork in a Beijing public school, this study demonstrated three key aspects of exclusions in migrant children's schooling experiences, namely, (1) access to school, (2) in-class participations and (3) peer interactions, and examined the "hidden curriculum" in the existing school practices that prevented migrant children from integrating successfully in the urban school settings. We found that academic performance lay at the root of social exclusions, but the local educators' perceptions of migrant children as outsiders, the urban-oriented school curricular and urban children's involvement (vis-à-vis migrant children's little involvement) in the extracurricular activities at school as well as the paid supplementary trainings outside school together formed the "hidden curriculum" that led to the marginalization of migrant students in the urban school system.