This study evaluated the efficacy of a preschool mathematics program based on a comprehensive model of developing research-based software and print curricula. Building Blocks, funded by the National Science Foundation, is a curriculum development project focused on creating research-based, technology-enhanced mathematics materials for pre-K through grade 2. In this article, we describe the underlying principles, development, and initial summative evaluation of the first set of resulting materials as they were used in classrooms with children at risk for later school failure. Experimental and comparison classrooms included two principal types of public preschool programs serving low-income families: state funded and Head Start prekindergarten programs. The experimental treatment group score increased significantly more than the comparison group score; achievement gains of the experimental group approached the sought-after 2-sigma effect of individual tutoring. This study contributes to research showing that focused early mathematical interventions help young children develop a foundation of informal mathematics knowledge, especially for children at risk for later school failure.