"Teaching Literacy in English to K-5 English Learners" discusses the importance of teaching English learners to read in English while they are developing oral proficiency, and how this helps them increase vocabulary, speak in English, and learn other subject-matter content. Specifically, it recommends and explains successful practices in 5 different areas based on solid research: assessment, small-group instruction, vocabulary instruction, academic English development, and cooperative learning.
Teaching Literacy in English to K-5 English Learners. U.S. Department of Education: Doing What Works. Washington, D.C.