This study examines the efficacy, cost, and implementation of an integrated science and literacy curriculum for kindergarten. The study was conducted in a large urban district and included 1,589 students in 71 classrooms in 21 schools. The research includes a multi-site cluster-randomized controlled trial and mixed-methods cost and implementation studies. Analysis revealed significant impacts on comprehension, letter-naming fluency, and motivation to read. No main impacts were observed on decoding, word identification, or writing; however, exploratory analysis revealed that students whose teachers implemented the treatment with fidelity performed statistically significantly better in writing and decoding. The cost to produce the observed effects was estimated at $480 per student, two-thirds of which was borne by the school. Despite this cost, treatment classrooms achieved savings by using an average of three fewer instructional programs than control classrooms. Teachers reported positive effects from the integrated curriculum on student engagement, learning, and behavior.