The primary purpose of the study was to determine if computer-based training programs promoted fluent and flexible use of reasoning strategies to solve addition problems using different tasks. Specifically, does participation in strategy training result in the fluent application of the target strategy on a traditional mental arithmetic task? Does participation in strategy training result in the flexible application of the target strategy on an alternative shortcut task? The research was conducted in five schools in two districts serving a mid-sized midwestern community. The findings of this study reveal the importance of near-doubles and make-ten strategies in achieving fluency with addition of single-digit number combinations. The intervention was effective in helping participants to move from developmental phase 1 (counting) to developmental phase 2 (reasoning) with near-doubles number combinations and developmental phase 3 (recall of specific facts or automatic reasoning strategies) with make-ten number combinations. In order to understand what constitutes the use of a shortcut strategy, there is a need to understand the foundation of these strategies. (Contains 1 figure and 4 tables.)