The analysis of 21,409 participants of the Early Childhood Longitudinal Study-Kindergarten cohort focused on home and school factors sought to understand the level of reading mastery that children experienced throughout elementary school and Grade 8 by relating home language use, timing of oral English language proficiency, and the provision of school-based English language learner services to reading mastery. Results confirm that non-English language use at home is associated with a decreased reading mastery at higher levels of proficiency in Grades 1 and 3, and is reduced to nonsignificance in Grades 5 and 8 with the inclusion of teacher and school factors. Also, the negative association between timing of oral English language proficiency and reading mastery is partially explained by teacher and school factors, particularly children's receipt of English language learner services. The findings provide support for policies that provide language services for language minority children and families during the transition to school and through the elementary school years.