Early mathematics knowledge is a strong predictor of later academic achievement, but children from low‐income families enter school with weak mathematics knowledge. An early math trajectories model is proposed and evaluated within a longitudinal study of 517 low‐income American children from ages 4 to 11. This model includes a broad range of math topics, as well as potential pathways from preschool to middle grades mathematics achievement. In preschool, nonsymbolic quantity, counting, and patterning knowledge predicted fifth‐grade mathematics achievement. By the end of first grade, symbolic mapping, calculation, and patterning knowledge were the important predictors. Furthermore, the first‐grade predictors mediated the relation between preschool math knowledge and fifth‐grade mathematics achievement. Findings support the early math trajectories model among low‐income children.