We report on the construction and application of an instrument entitled the "Science Achievement Influences Survey" to assess combined effects of student attitudes about science, peer interaction, and home support, and the frequency of student-centred and teacher-centred instructional practices on student achievement. Controlling for pre-test content knowledge, results indicated that student-centred teaching practices have a positive association with student achievement (p less than 0.01; i.e., group experiments) and a negative association with teacher-centred teaching practices (p less than 0.01; i.e., copying notes). Additionally, student attitudes about science were positively associated with student-centred teaching practices (p less than 0.01) and negatively associated with teacher-centred teaching practices (p less than 0.01). Most significantly, this study documents the predicted gains in science achievement associated with frequency of specific instructional practices used by middle-school science teachers. Especially noteworthy and significant is the finding that near-daily implementation of group experiments and reduction of extensive note-copying during class yield the greatest positive impact on student achievement. Outside of school, peer interaction and home support were not significantly associated (p greater than 0.05) with student achievement. The student sample included 611 middle-school science students with a wide range of socioeconomic and cultural backgrounds. (Contains 4 tables, 3 figures and 3 notes.)