An exploratory, comparative study of the achievement of 186 homogeneously and heterogeneously grouped second graders found no significant differences in overall achievement in reading and mathematics. However, a significant difference in reading comprehension scores of children in the two groups was found. At low, medium, and high academic performance levels, homogeneously grouped second graders scored significantly higher in reading comprehension than did heterogeneously grouped students. Children in homogeneous classes also exhibited significantly higher amounts of time-on-task than did children in heterogeneous classes. No difference across groups was found in time-on-task for high level children. If grouped homogeneously, low-achieving and middle-achieving children spent significantly more time-on-task. Time-on-task of second graders in homogeneous groups correlated significantly with their achievement in both reading and mathematics. This relationship was not observed for children in the heterogeneous groups. Among children grouped heterogeneously, but not homogeneously, preferences for auditory-visual learning stimuli were correlated with reading and mathematics achievement. Structure as a preferred learning style was negatively correlated with achievement in mathematics for children taught in homogeneous groups. Responsibility as a learning style was correlated with reading achievement for children taught in heterogeneous groups. Implications of the findings are discussed. (RH)