Two experiments were conducted to investigate the eVects of practice on strategy selection and strategy eYciency in mental arithmetic. Participants had to solve simple addition or multiplication problems, after having received 0, 3, or 6 practice sessions (Experiment 1), and before and after having received 3 practice sessions (Experiment 2). Strategy selection was measured by means of trial-by-trial strategy reports, whereas strategy eYciency was measured by means of response latencies. Results showed signiWcant practice eVects on retrieval frequency, procedural frequency, retrieval eYciency, and procedural eYciency. However, practice eVects on strategy eYciency appeared to be both strategy-speciWc (i.e., only for procedural strategies) and operation-speciWc (i.e., only for multiplication problems). Implications of the present results for mathematic cognition and its modeling are discussed.