English learners face challenges that are compounded by the fact that they enter schools at every grade level and at various times during the academic year with varying levels of language and literacy proficiency in both their native language and English. This chapter describes four randomized, controlled trials (RCTs) including long-term follow-ups designed to evaluate the efficacy of an English and Spanish supplemental intervention for bilingual (Spanish/English) first graders with reading difficulties. It presents an overview of the English and then Spanish interventions. This is followed by a summary of four studies, which were implemented in successive years in Houston, Austin, and Brownsville. Students were randomly assigned to treatment or comparison conditions. At the end of first grade, all four experimental studies reported improved outcomes for intervention students on phonological awareness, word-reading fluency, reading comprehension, and spelling, and these findings were maintained through fourth grade for treatment students.