This study examined student readiness to learn and teacher effectiveness in order to determine their impact on middle grades mathematics achievement. Survey data were collected from 964 middle grades students and 93 mathematics teachers in Texas. This study is the first to use this particular collective efficacy short form with middle grade students, and factor analyses were conducted accordingly. Hierarchical linear modeling was used to measure the relationship between teacher perceptions of student readiness to learn and student perceptions of teacher effectiveness on mathematics achievement in the middle grades. The results of these analyses indicated that students' perceptions of teacher effectiveness and teachers' perceptions of student readiness to learn each made a significant contribution to the variance in middle grades mathematics achievement. Implications are discussed.