In a longitudinal group-randomized trial, we explore the key role of the quality of classroom text discussions in mediating the effects of Content-Focused Coaching (CFC) on student reading achievement (2983 students, 167 teachers). Schools in the United States serving large numbers of minority and English language learning (ELL) students from low-income families were randomly assigned to participate in the CFC literacy-coaching program or to continue with the literacy coaching that was standard practice for the district. The findings identified a positive effect of the CFC program on observed classroom text discussion quality. Supporting the theory underlying CFC, the positive effect of the program on student reading achievement was mediated through the quality of classroom text discussions. Students' language status moderated the direct effect of the program, with stronger effects for ELL students compared to their English-proficient peers. (Contains 2 figures and 9 tables.)