This study explored to what extent two groups of mainstream teachers in the midwestern region of the USA with differing degrees of English Language Learner (ELL) specific universitypreparation reportedly engaged in practises that incorporated the native languages (L1) of ELL students in instruction. The study further examined specific strategies reported by mainstream teachers in promoting L1 use in instruction as well as challenges identified in implementing this practise. The study utilized a mixed-method design that included analyses of survey data from a quantitative study (n=227) and qualitative analyses of teacher discourse from course documents and open-ended survey questions. Findings indicated that while both groups of teachers reportedly engaged in practises that promoted L1 use in instruction to some extent, teachers with at least three courses of ELL-specific university preparation appeared to engage in these practises to a much greater extent than those without such preparation. This paper explores the implications of results from this study for teacher education programmes in the USA with the responsibility of preparing teachers to effectively serve growing numbers of culturally and linguistically diverse student populations.