Analyzing Early Childhood Longitudinal Survey--Kindergarten (ECLS-K) data, we examine how exposure to instructional practices influences math test scores at the end of kindergarten for children from different racial/ethnic and socioeconomic backgrounds, and for children with different levels of math skills at kindergarten entry. We also analyze the relationship between socioeconomic background and math academic readiness within racial/ethnic categories. Our results demonstrate that race/ethnicity and levels of math academic readiness moderate the relationship between instructional practices and math achievement. While we find that interactive group activities enhance students' mathematics achievement in kindergarten and that drills enhance math academic achievement of students with high math academic preparedness in kindergarten, we also find that use of manipulatives as well as music and movement have significant negative effects on mathematics achievement of Black students. Given the importance of kindergarten for launching children onto successful academic trajectories, the findings have implications for addressing racial/ethnic and socioeconomic status gaps in mathematics achievement.