This study examined teachers' language use across the school year in 6th grade urban middle-school classrooms (n = 24) and investigated the influence of this classroom-based linguistic input on the reading comprehension skills of the students (n = 851; 599 language minority learners and 252 English-only) in the participating classrooms. Analysis of speech transcripts revealed substantial variability in teachers' use of sophisticated vocabulary and total amount of talk and that individual teacher's language use was consistent across the school year. Analyses using Hierarchical Linear Modeling showed that when controlling for students' reading comprehension and vocabulary knowledge at the start of the year, teachers' use of sophisticated vocabulary was significantly related to students' reading comprehension outcomes, as was the time spent on vocabulary instruction. These findings suggest that the middle school classroom language environment plays a significant role in the reading comprehension of adolescent learners.