This exploratory, qualitative study examines the foundational knowledge and instructional methods needed for academic language teaching of English language learners (ELLs). It also examines how mentoring practices can build secondary content-based novice teachers' instructional capacity in this area. The study uses synthesized data from two independent studies to contextualize findings on essential instructional practices within the process of mentoring new teachers. Three themes emerged: novices need the foundational, theoretical and practical knowledge underlying essential practices for academic language development; essential practices must be articulated in detail for enactment by teachers; and balancing explicit and immersive academic language instruction is a major paradigm shift for novices. Implications for mentor and teacher professional development are discussed, as mentors are key to supporting the uptake of dynamic instructional methods needed to enact essential practices. While mentoring is a common strategy for supporting new teachers, few models exist for how mentors can support new teachers with building the academic language development of ELLs. Further, few studies examine mentoring exchanges that can promote teachers' understanding and practices to support ELL students' academic language development. Limitations of the study include sample size and use of varied respondent data sets.