The widespread concern about mathematics achievement has drawn extensive research attention to what skills predict later academic achievement. There is clear and consistent evidence that math achievement at school entry is the strongest predictor of later school success and educational attainment. Early childhood math achievement can thus have far-reaching effects on students' schooling. Using longitudinal data from a low-income sample of preschoolers, the authors identify specific preschool mathematical competencies and relate them to later math achievement for students of low-income and minority backgrounds. This study is a secondary data analysis of data collected from the Technology-enhanced, Research-based, Instruction, Assessment, and professional Development (TRIAD) intervention evaluation study, which assessed the impact of an early mathematics intervention in low-resource schools. The full sample consisted of 1375 students in the fall of the preschool year. This analysis employs a sub-sample of children (n = 781) who had valid mathematics achievement score data in pre-kindergarten and fifth grade. The current study utilizes data collected during preschool, kindergarten, 1st, 4th, and 5th grade. The authors use multivariate regression analyses to relate end of pre-k math skills to math achievement to later grades in elementary school. The results reported in this study, along with a growing body of research with converging data, lend support to strengthening the link between promoting math skills in early childhood education and elementary school mathematics for later success. Tables are appended.