This study evaluated the effects of cooperative learning on students' verbal interaction patterns and achievement in a conceptual change instructional model in secondary science. Current conceptual change instructional models recognize the importance of student–student verbal interactions, but lack specific strategies to encourage these interactions. Cooperative learning may provide the necessary strategies. Two sections of low-ability 10th-grade students were designated the experimental and control groups. Students in both sections received identical content instruction on the particle model of matter using conceptual change teaching strategies. Students worked in teacher-assigned small groups on in-class assignments. The experimental section used cooperative learning strategies involving instruction in collaborative skills and group evaluation of assignments. The control section received no collaborative skills training and students were evaluated individually on group work. Gains on achievement were assessed using pre- and posttreatment administrations of an investigator-designed short-answer essay test. The assessment strategies used in this study represent an attempt to measure conceptual change. Achievement was related to students' ability to correctly use appropriate scientific explanations of events and phenomena and to discard use of naive conceptions. Verbal interaction patterns of students working in groups were recorded on videotape and analyzed using an investigator-designed verbal interaction scheme. The targeted verbalizations used in the interaction scheme were derived from the social learning theories of Piaget and Vygotsky. It was found that students using cooperative learning strategies showed greater achievement gains as defined above and made greater use of specific verbal patterns believed to be related to increased learning. The results of the study demonstrated that cooperative learning strategies enhance conceptual change instruction. More research is needed to identify the specific variables mediating the effects of cooperative learning strategies on conceptual change learning. The methods employed in this study may provide some of the tools for this research.