The significant home price premium in top school attendance zones and the emerging evidence on residential segregation found in China's cities call for a study on the socioeconomic segregation in urban schools and its potential consequences. Using the 2009 and 2012 Programme for International Student Assessment (PISA) surveys, this paper documents the socioeconomic and academic segregation among 15-year-old students in middle and high schools in Shanghai. We illustrate the effects of residence-based enrollment by comparing middles schools (required to use residence-based enrollment) and high schools (allowed to use merit-based selection), and further quantifies the relationship between school socioeconomic composition and academic achievement. We find that middle schools are more socioeconomically segregated, while high schools are more academically segregated. However, school segregation lessened from 2009 to 2012, especially in middle schools, likely due to the weakening of residence-based enrollment. Public schools in Shanghai became somewhat more integrated socioeconomically, but such a progress in equity was accompanied by an increasingly positive correlation between individual socioeconomic background and student performance, and an increasingly negative correlation between school socioeconomic diversity and student performance, both requiring the attention of policymakers.