Computer technology, when coupled with reform-based teaching practices, has been shown to be an effective way to support student learning of mathematics. The quality of the technology itself, as well as how it is used, impacts how much students learn. Interactive simulations are dynamic virtual environments similar to virtual manipulatives that also make use of implicit scaffolding, targeted feedback, and concept-focused games. This study examines the effect of teaching mathematics with an interactive simulation on student attitudes and achievement. The intervention involved two classes of fourth-grade students using the interactive simulation over the course of four days to learn early fraction concepts. Data sources included pretests and posttests, a student attitude survey, and student focus group interviews. Significant changes were found from pretest to posttest on overall fraction knowledge, as well as on procedural and conceptual knowledge. Student attitudes toward learning fractions with the interactive simulation were overwhelmingly positive, and these findings were supported by the focus group interview data. These results suggest that interactive simulations, when paired with effective teaching, can be highly effective tools for supporting both procedural and conceptual understanding.