Accumulating research has established explicit mathematics instruction as an evidence-based teaching practice. This study utilized observation data from a multi-year efficacy trial to examine the longitudinal effect of a core kindergarten mathematics program on the use of explicit mathematics instruction among two distinct groups of teachers: one group that used standard practices in Year-1 of the efficacy trial and the core program in Year-2, and a second group that used the core program in both years. Targeted teaching practices consisted of teacher models, student practice opportunities, and teacher-provided academic feedback. Implementation of the program in Year-2 was found to increase the mean rates of teaching practices of teachers who used standard teaching practices in Year-1. Effect sizes are also suggestive of a positive impact of a second year of implementation with the core program. Implications for designing explicit mathematics programs and investigating evidence-based practices in future research are discussed. [This paper was published in "Learning Disability Quarterly" v41 n3 p144-158 Aug 2018 (EJ1185339).]