This study examines the relationship between early number competence and later mathematics achievement in children from kindergarten to third grade. The research found that children's number competencies at the beginning of kindergarten strongly predicted their mathematics performance and growth over the next two years. Specifically, higher levels of kindergarten number competence were associated with better mathematics achievement at the end of third grade, and faster growth in number competence predicted higher levels of mathematics achievement. The study also found that low-income children performed worse in mathematics and progressed more slowly compared to middle-income children, but their poor performance was mediated by their weaker kindergarten number competence. Additionally, older children performed better in mathematics due to their stronger kindergarten number competence. The findings highlight the importance of early number competence in setting children's learning trajectories in elementary school mathematics and suggest that interventions targeting number competence should be prioritized in early education.This study examines the relationship between early number competence and later mathematics achievement in children from kindergarten to third grade. The research found that children's number competencies at the beginning of kindergarten strongly predicted their mathematics performance and growth over the next two years. Specifically, higher levels of kindergarten number competence were associated with better mathematics achievement at the end of third grade, and faster growth in number competence predicted higher levels of mathematics achievement. The study also found that low-income children performed worse in mathematics and progressed more slowly compared to middle-income children, but their poor performance was mediated by their weaker kindergarten number competence. Additionally, older children performed better in mathematics due to their stronger kindergarten number competence. The findings highlight the importance of early number competence in setting children's learning trajectories in elementary school mathematics and suggest that interventions targeting number competence should be prioritized in early education.