This mixed-methods study was used to examine the impact of teachers’ self-efficacy beliefs and instructional practices when teaching English Language Learners (ELLs). Quantitative and qualitative data were sequentially collected, concurrently analyzed, and triangulated. A sample of 126 experienced K-12 educators from the northeastern US completed (a) a demographic survey, (b) a teachers’ self-efficacy survey, and (c) a classroom strategy scale. A stepwise multilinear regression procedure determined that teachers’ use of academic performance feedback, efficacy beliefs in student engagement, and employment of both student-directed and direct instructional practices predicted teachers’ self-perceptions about being able to adapt instruction for their ELL population. Qualitative data were obtained from 10 participants who self-rated as having high self-efficacy and classroom strategy use. Themes included foundational requirements, school leadership, specific instructional strategies, and knowing how to apply these strategies with ELLs. The triangulated results revealed that when school leaders provide professional learning opportunities that support a truly inclusive curriculum and collaborative time in which to plan with colleagues, there is a positive impact on teachers’ self-efficacy to instruct ELLs.