Although mathematics development research has become more prominent in the school psychology literature in recent years, a large research gap in this area exists regarding English language learners (ELLs). Significant research in education, cognitive science, and psychology has been devoted to understanding the links between language and mathematics, but the developmental factors that predict stability and change in mathematics skill development among ELLs are less clear. In one study, I investigated growth and change among ELLs compared to English-proficient student (EPS) peers using latent change score modeling to detect differences in interindividual and intraindividual change across language proficiency groups. I also examined the extent to which working memory differentially predicts mathematics change trends and patterns across language groups. In a second study, I closer examined the processes of mathematics development among ELLs by investigating the presence of heterogeneous, unobserved growth trajectories; whether development of English language proficiency (ELP) predicts mathematics growth patterns; and the interaction between working memory and language proficiency gains in predicting later mathematics growth. Results from Study 1 suggested that ELLs and their English-proficient peers change similarly across time though at different levels of performance. Additionally, kindergarten working memory operated similarly in predicting growth parameters among both ELL and EPS subpopulations. Findings from Study 2 are suggestive of a single highly variable growth trajectory among ELLs. Although working memory uniquely predicted mathematics developmental patterns, interactions between working memory and English proficiency gains were not predictive of later mathematics level or change pattern. However, gains in English early reading skills (arguably one domain of ELP) uniquely and positively predicted later mathematics performance level, although that advantage was partially offset by a prediction of decelerating mathematics growth through fourth grade. Theoretical and practical applications for research involving ELLs in the context of RTI, future directions, and limitations are discussed.