This investigation examined whether teacher practices, as measured by the Classroom Strategies Assessment System (CSAS), were associated with students' proficiency and gain scores, as measured by the Measure of Academic Progress (MAP), in 13 high-poverty charter schools in New Jersey. Results from two-level hierarchical linear models, fitted to a sample of 2,188 Kindergarteners through eighth-grade students in 110 classrooms, revealed that instructional and behavior management strategies on the CSAS were associated with (a) MAP gains in mathematics but not in reading and (b) MAP Rasch Unit (RIT) (proficiency) scores in mathematics and reading. The relationship between CSAS scores and student achievement did not differ across grade levels. In general, students in classrooms with higher quality use of classroom strategies exhibited higher gains in mathematics and proficiency scores in mathematics and reading. Implications for research and educational practices are discussed.