Fifth and seventh-graders accomplished computational estimation tasks in conditions where only one versus two strategies were available. Children were told which strategy to execute on each problem. Results showed that both groups of children were faster under one-strategy condition than under two-strategy condition and that age-related differences in performance were larger under two-strategy condition. Also, differences in strategy performance tended to vary as a function of the number of strategies, and this strategy difference was largest in younger children. These findings have implications to further our understanding of strategy execution in arithmetic and in other cognitive domains, as well as of age-related differences in children’s performance during cognitive development.