This longitudinal study tests the optimal placement of cooperative learning during instruction. Pre-service teachers (N = 97) were taught about psychology theories applied to educational contexts and were asked to apply this knowledge in problem-solving activities using relevant classroom cases. Participants were assigned to either (Early) or (Later) cooperative group (factor 1). In the former, the learners first encountered problem-solving case questions in cooperative groups, and the latter first engaged in independent problem solving, then cooperative groups. To draw out the importance of timing as it relates to cooperation, we also included a second factor, where the participants were assigned to either a group (Cooperation) or an individual condition (Control). Results confirm the benefits of cooperation over individual work and suggest that timing cooperative discussions after initial independent problem solving for students in cooperative groups result in more desirable outcomes, but that timing is less influential when students work alone.