As the use of project-based learning becomes more frequent in the K-12 science classroom, and in chemistry classrooms in particular, teachers have begun to identify practical questions about implementation that should be addressed empirically. One such question concerns whether there is an ideal group size that fosters individual student achievement. The current project was designed to assess how group size might impact student chemistry content learning in a project-based learning environment, and how well students are prepared to transfer this new knowledge to other relevant areas. The results indicated that particular conditions (e.g. advanced classrooms) interact with group size (a seemingly superficial feature) to differentially influence the depth and level of student learning related to the unit and student's ability to transfer his/her knowledge outside of the context of a project-based learning unit.