The purpose of this study was to examine the effects of curricular (textbook, revised, and differentiated) and grouping (whole, between, and within-class) practices on intermediate students' achievement in mathematics. A pretest-posttest, quasi-experimental design using a stratified random sample of 31 teachers and their students (N = 645) was used in this study. Achievement data were collected using a curriculum-based assessment. Repeated measures analysis of variance was employed to investigate the effects of grouping arrangements and curricular design on the treatment and comparison group posttest scores. Results indicated significant differences, F (5, 246) = 22.618, p less than 0.001, between comparison and revision treatment groups on the posttest after adjusting for grade level (4 or 5). Further results indicated significant differences, F (11, 673) = 41.548, p less than 0.001, among all treatment groups after adjusting for grade level. Comparison of Textbook, Revised, and Differentiated Unit is appended. (Contains 6 tables.)