In the US, public school teachers are currently experiencing an unprecedented increase in the number of English language learner (ELL) students with whom they work. Research shows the practice of incorporating ELL students’ native languages (L1) into instruction to be a major factor enhancing their success in school. In this study, 327 pre-service and experienced mainstream teachers in the midwestern region of the USA were surveyed on their perspectives related to this practice. Findings from descriptive analyses indicated that while teachers generally supported L1 use in instruction, they tended to show stronger support for its underlying theory than for its practical implementation. Results from a series of analyses of variances (ANOVA) suggested a clear link between English as a second language specific university preparation and an increased support for the theory and practice of L1 use in instruction. Results further suggested links among some combination of teaching experience and an increase in support for this practice. Findings from this study are discussed in relation to strategies and directions for teacher educators with the responsibility of preparing mainstream teachers to effectively serve ELL students in regions of the USA with unprecedented increases in culturally and linguistically diverse student populations.