The purpose of this study was to examine the effects of heterogeneous and homogeneous grouping on the mathematical achievement of students in third grade. Participants were 16 third graders in a self-contained classroom, assigned to either small homogeneous or heterogeneous group for math instruction for 7 weeks. Pretest-posttest scores and growth…

The purpose of this study was to examine third-grade student achievement in mathematics and reading for students who were in skill groups, as compared to those who were traditionally grouped, with student attendance being taken into consideration as a variable of additional comparison. Skill groups are a type of flexible ability grouping, where…

Defining causal effects as comparisons between marginal population means, this article introduces marginal mean weighting through stratification (MMW-S) to adjust for selection bias in multilevel educational data. The article formally shows the inherent connections among the MMW-S method, propensity score stratification, and…