This article focuses on cluster teachers' differentiation of their classroom instructional practices within an urban setting. Data were gathered from classroom observations of the learning task, questioning, and the classroom environment; ratings of observations using the "Classroom Instructional Practices Scale;" and interviews with teachers, parents, and students. Ten observers assessed the differentiation of classroom instructional practices in literacy and mathematics of 79 cluster classrooms in 18 different elementary/intermediate schools. Results indicated the majority of cluster teachers used a standardized guide in structuring their curriculum, created positive learning environments, and varied their learning activities. Teachers appeared to need permission for flexibility and professional development for implementing acceleration, varying activities for individual students within small groups, varying time for learning, managing behavior of multiple groups and independent learning, making connections across subject areas to learning outside of school, and understanding the characteristics and role of gifted students in the classroom. Some system practices were also identified as creating obstacles for differentiation.