China’s unprecedented rural-urban migration adds profound complications to the entrenched rural-urban spatial inequality in the cognitive and emotional development of middle schoolers. Despite the nine-year compulsory education law, parents’ rural-urban migration and institutional barriers of rural household registration (hukou) have created “brought-along” (to cities) and “left-behind” (in villages) student bodies. While governments and schools gradually adjust policies and measures to serve these fast growing, sizable, nontraditional student bodies, these students may be growing up with delayed development. We capitalize on the global curriculum-dependent achievement in math, Chinese, and English, curriculum-independent cognitive test IRT scores, and social emotional assessments of a nationally representative sample of 10,279 7th graders in 221 classrooms, 112 schools in 2013-14. This paper examines whether and how school institution’s responsiveness to rural-urban migration plays a decisive role in reshaping the disparities in the cognitive and emotional development of middle schoolers in China.