Using a cluster randomized trial design, we evaluated the persistence of effects of a research-based model for scaling up educational interventions. The model was implemented in 42 schools in two city districts serving low-resource communities, randomly assigned to three conditions. In pre-kindergarten, the two experimental interventions were identical, but one included follow-through in the kindergarten and first-grade years, including knowledge of the pre-K intervention and ways to build upon that knowledge using learning trajectories. Students in the experimental group scored significantly higher than control students ("g" = 0.51 for those who received follow-through intervention in kindergarten and first grade; "g" = 0.28 for non-follow-through), and follow-through students scored significantly higher than non-follow-through students ("g" = 0.24). (Contains 6 tables and 1 note.)