In this article we examine how students engage in learning mathematical concepts in the middle grades of an urban public school in the Southwestern United States. In the context of a 3-year National Science Foundation-funded longitudinal study of the development of students' rational number understanding, we encountered differing levels of engagement among urban youth. We found that these levels of engagement are a byproduct of classroom teachers' practices and their expectations for student work in a high poverty, primarily Latino neighborhood school. This article describes ways in which classroom culture, including instruction and teacher expectations, influence the nature and extent of students' experiences and engagement in the middle school mathematics learning environment.