As K-12 schools in the United States continue to experience increases in enrollment of English learners (ELs), educators and researchers seek to identify effective teaching practices. Previous research in the area of teacher effectiveness with ELs has focused mainly on pre-service and elementary-level teachers, with studies of coursework and background and contextual factors that influence their self-efficacy in providing high-quality instruction. Limited research has focused on the specific knowledge and skills useful for secondary-level teachers tasked with developing their students' language skills through the delivery of disciplinary curricula. To address the gap in the literature, a hermeneutic phenomenological study design was employed to explore what meaning secondary content area teachers ascribe to high self-efficacy and effective teaching practices with English learners in mainstream classrooms. Major themes that emerged from in-depth interviews with nine secondary teachers of mathematics, science, or social studies included (a) ethic of care, (b) overcoming a lack of EL preparation, (c) undercover advocate, and (d) culturally responsive pedagogy. A common thread interwoven through all narratives was leveraging students' native languages through translating and translanguaging practices and scaffolding language and literacy development. Findings will contribute to the emergent scholarship on content and language integration in secondary mainstream classes and yield a more precise understanding of teacher effectiveness with a diverse EL population. Implications are provided regarding policy and program decisions for teacher preparation in higher education, district recruitment and professional development, and state-level certification. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]