The extent to which teachers implement evidence-based practices, such as explicit instruction, is critical for improving students' mathematics achievement. The purpose of this study was to examine the effect of the kindergarten "Early Learning in Mathematics" (ELM) curriculum on teachers' use of explicit mathematics instruction in core educational settings. Observation data for the study were collected during a randomized controlled trial designed to investigate the efficacy of the ELM curriculum. A multifaceted observation system was used to examine teachers' provision of high-quality and intensive instructional interactions during core mathematics instruction. A total of 379 observations were conducted in 129 classrooms (68 treatment and 61 comparison), involving approximately 2,700 students from 46 schools in Oregon and Texas. Results indicate that ELM classroom teachers delivered significantly higher rates of practice opportunities for individuals and groups of students compared with comparison classroom teachers who implemented standard district mathematics instruction. Implications for instruction are discussed.