The active learning literature has greatly expanded over the past few years. This article investigates the utility of employing concept map activities in a medium-sized class, and whether or not it improves students' learning and retention of material. We find that concept mapping activities significantly enhance students' mastery and recollection of class material. The size of the effect is considerably greater in our treatment group, relative to our control group. We discuss the advantages of this specific active learning technique, and offer suggestions for its incorporation into different institutional settings.