This study used the Eccles et al. expectancy-value (E-V) theory to test the influence of motivation on mathematics achievement and enrollment using data from a cohort of 926 seventh-grade prealgebra students (49% male, 76% Hispanic, 76% low income, and 55% English learner). E-V beliefs were assessed in seventh grade along with achievement, and enrollment was measured in eighth grade. Differential associations of motivation, achievement, and enrollment were examined across Hispanic and non-Hispanic populations. Expectancy for success and task value uniquely predicted seventh-grade achievement and eighth-grade algebra enrollment after controlling for prior achievement and a full set of demographic controls, including low socioeconomic status and English fluency. The association of interest value and achievement differentiated across Hispanic and non-Hispanic youth, suggesting that the effect of interest value on mathematics achievement was weaker for Hispanic youth than for non-Hispanics after accounting for success expectations and prior achievement.