This study explores whether teachers and students are influenced by the size of the inner-city elementary school to which they belong. Focusing on teachers' attitudes about their responsibility for student learning and students' l-year gains in mathematics achievement scores, we used data from almost 5,000 teachers and 23,000 sixth and eighth-grade students in 264 K-8 Chicago schools. The data were collected through 1997 surveys and annual standardized tests. We employed hierarchical linear modeling (HLM) to estimate school effects. On both outcomes, small schools (enrolling fewer than 400 students) are favored compared with medium-sized or larger schools. In small schools, teachers have a more positive attitude about their responsibility. for students' learning and students learn more. Even after taking size into account, learning is also higher in schools with higher levels of collective responsibility. Thus, we conclude that school size influences student achievement directly and indirectly, through its effect on teachers' attitudes.