This study investigates whether using My Math Academy, which provides personalized content and adaptive embedded assessments to support existing curricula, can improve learning outcomes and engagement for kindergarten and first grade students (N = 505 treatment, 481 control). Findings indicate that students using My Math Academy made significant learning gains in math relative to children who did not. More skills mastered in My Math Academy was associated with greater learning gains on the external assessment, with the greatest impacts among students with lower levels of math knowledge, where there was more room for growth and on the most difficult skills. Teachers surveyed found My Math Academy easy to use in their classrooms and recognized it as a valuable learning resource that supplemented their existing curricula to improve students' engagement, motivation, and confidence in learning math.