Due to the socioeconomic status-related gap in early mathematical knowledge and the need to improve low-income children's readiness for school mathematics, the authors developed an intervention, "Pre-K Mathematics", and rigorously evaluated it over several studies. This math intervention has been found to be highly effective at improving pre-k children's mathematical knowledge relative to a control group. In this presentation, the authors examine the pre-k mathematics intervention implemented at a customary level of scale and at a distance from the developer. Analyses will examine (1) effectiveness at scale across varied contexts, and (2) classroom practices that mediate, at least in part, effective math outcomes for young children.