Due in part to the challenges associated with learning a new language, English language learners (ELLs) typically begin school with lower achievement than their non-ELL peers, and those achievement gaps often close slowly if at all. A separate body of research shows that achievement is associated with social-emotional learning constructs like self-efficacy, yet this relationship has rarely been examined for ELLs. In this study, multivariate models that jointly estimate growth in achievement and self-efficacy during middle school are used to see how underlying developmental processes relate for ELLs. Results indicate that self-efficacy tends to decline for all students despite growth in math and reading, and that achievement and self-efficacy are much lower for ELLs. Further, there is evidence that slower growth in math and reading for ELLs is associated with their low self-efficacy at the beginning of middle school (self-efficacy mediates the association between ELL status and achievement growth). Implications for closing achievement gaps between ELLs and non-ELLs are discussed.