In this paper, we argue that computational models of learning can contribute precise theory to explain surprising student learning phenomena. In some past studies, practice produces better learning than studying examples, whereas other studies show the opposite result. We explain this contradiction by suggesting that retrieval practice and example study involve different learning cognitive processes, memorization and induction, and each process is optimal for different types of knowledge. We implement and test this theoretical explanation by extending an AI model of human cognition to include both memory and induction processes and comparing the behavior of the simulated learners to those of human participants. We show that the behavior of simulated learners with forgetting matches that of human participants better than simulated learners without forgetting. Simulated learners with forgetting learn best using retrieval practice in situations that emphasize memorization (such as learning facts), whereas studying examples improves learning when multiple pieces of information are available, so induction and generalization are necessary (such as learning skills).