Factors affecting performance on base-10 tasks were investigated in a series of four studies with a total of 453 children aged 5-7 years. Training in counting-on was found to enhance child performance on base-10 tasks (Studies 2, 3, and 4), while prior knowledge of counting-on (Study 1), trading (Studies 1 and 3), and partitioning (Studies 1 and 4) were associated with enhanced base-10 performance. It emerged that procedural knowledge of counting-on, trading, and partitioning can lead to improvements in procedural knowledge of the base-10 system. The findings lend support to the model of iterative development of conceptual and procedural knowledge advanced by Rittle-Johnson et al. (2001).