This study used a randomized field trial design to evaluate the efficacy of a research-based model for scaling up an intervention focused on preschool mathematics. Although the successes of research-based educational practices have been documented, equally well known is the paucity of successful efforts to bring these practices to scale. The same research corpus provides guidelines to scale up successful interventions. We designed an intervention model based on that research, including mathematics curricula with an emphasis on teaching for understanding following developmental guidelines, or learning trajectories, and using technology at multiple levels. We then implemented that model and evaluated the implementation with a limited scale up study. Within a design involving 25 classrooms serving children at risk for later school failure, we examined the impact of the model, using measures of fidelity of implementation, classroom observations of mathematics environment and teaching, and child outcomes. High levels of fidelity of implementation resulted in consistently higher scores in the intervention, compared to control, classes on the observation instrument and significantly and substantially greater gains in children's mathematics achievement in the intervention, compared to the control, children (effect size = 0.62). (Contains 5 tables.)