This study analyzed relationships between students' regard for one another and their mathematics achievement in cooperative learning groups in six grade 7 middle school classes. The sample consisted of 184 students (55% Hispanic, 14% Black, 27% White, 3% Asian American) in a city of Los Angeles County. Two teachers each taught three classes, two experimental, one comparison. Teacher difference emerged as the central finding of the study. Overall, students increased their regard for teammates but there was no significant increase in mathematics achievement and no correlation between regard and mathematical achievement. Observation of the classes revealed that despite the fact that the two teachers participated in the same training sessions in preparation for small group work and used identical curriculum, three factors emerged that may have contributed to the different findings for the two teachers: seating arrangements, teacher style, and instruction. This study shows that there can be a positive relationship between regard and mathematics achievement but that the teacher plays a very important role in the process. Second, there are important implications for the education of teachers. Contains 30 references. (MKR)