Three experiments examined testing effects on learning of natural concepts and metacognitive assessments of such learning. Results revealed that testing enhanced recognition memory and classification accuracy for studied and novel exemplars of bird families on immediate and delayed tests. These effects depended on the balance of study and test trials during training. Metacognitive measures provided results suggesting that participants were aware of the beneficial effects of testing. A new measure of metacognition at the level of categories is introduced and shown to be potentially useful for theory and applied purposes. It is argued that focusing on optimizing the learning of natural concepts encourages the convergence of theorizing about memory, concept learning, and metacognition and holds promise for the development of applications to education. (Contains 5 tables, 1 figure and 1 footnote.)