This study examines cognitive and social processes in group interactions that shape collaborative learning in science classrooms. Three small groups of students were observed while working collaboratively on explaining the burning of a candle under a jar. The learning environment served as a context for examination of conceptual convergence, a process wherein students construct shared meanings for science concepts through gradual refinement of ambiguous, partial meanings presented in group space. Despite engaging in the same activity with very similar instructional supports, the groups displayed very different patterns of interaction and achieved varied degrees of conceptual convergence. One group collaborated effectively and displayed evidence of individual conceptualizations of science content converging to establish a more well-informed shared conceptualization. The other groups were not as successful, each for unique reasons. Problems demonstrated in one group included lack of self-confidence, poor monitoring of group learning, and active avoidance of potentially fruitful conceptual conflicts. The other group struggled primarily because of a combative social context. The major educational significance of this study was the identification of social context and interactive patterns, group approaches to conceptual conflicts, and instructors' roles in collaborative activities as crucial aspects of productive group learning. (Contains 2 tables and 1 figure.)