Early education is replete with debates about "academic" versus "play" approaches. We evaluated 2 interventions, the "Building Blocks" (BB) mathematics curriculum and the BB synthesized with scaffolding of play to promote executive function (BBSEF), compared to a business-as-usual (BAU) control using a 3-armed cluster randomized trial with more than 1,000 children in 84 preschool classrooms across three districts (multiracial or multiethnic, low income, 27% English Language Learner). Impact estimates for BBSEF were mixed in sign, small in magnitude, and insignificant. Most impact estimates for BB were positive, but only a few were statistically significant, with more in the kindergarten year (delayed effects), including both mathematics achievement and executive function (EF) competencies. Gains in both mathematics and EF can be mutually supportive and thus resist the fade-out effect.