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 age 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. Further, 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. [At time of submission to ERIC this article was in press with "Child Development."]