The purpose of this study was to discover if grouping students in the laboratory on the basis of their formal reasoning ability affected (1) their science content achievement, (2) their formal reasoning ability, (3) the learning environment in the laboratory, and (4) the relationships between individuals in a particular group. The laboratory groups for three physical science classes for preservice elementary teachers were arranged as follows: (1) one class with students of unequal reasoning ability grouped together, i.e., one highly developed formal reasoner per group (the heterogeneous group), (2) one class with students of similar reasoning ability grouped together (the homogeneous group), and (3) one class arranged in groups according to the desires of the class members (the student choice group). The three classes were compared using pre-and post-scores on content and formal reasoning instruments and scores for classroom environment and social relationships. Results indicated that the groupings as described had significantly different effects on science content achievement but not on any of the other questions posed above. The students in the class with laboratory teams grouped by student choice had significantly lower science content scores than the students in the classes with teams formed using either the heterogeneous or homogeneous grouping procedures. The difference between the heterogeneously and homogeneously grouped classes was not significant at the 0.05 level.