This investigation tested the importance of early academic achievement for later achievement trajectories among 18,011 students grouped by level of socioeconomic risk. Students considered to be at highest risk were those who experienced homelessness or high residential mobility (HHM). HHM students were compared to others eligible for free meals, students eligible for reduced price meals, and students who were neither HHM nor low-income. Socioeconomic risk and oral reading ability in first grade predicted growth of reading and math achievement in grades 3 through 8. Risk status predicted achievement beyond the effects of early reading scores and also moderated the prediction of later growth in reading achievement from early oral reading. Results underscore the early emergence and persistence of achievement gaps related to poverty, high and accumulating risk for HHM students, and the significance of oral reading in first grade, both as an early indicator of risk and also as a potential protective factor.