This study investigated the relation between teachers' (N = 22) use of sophisticated and complex language in urban middle-school classrooms and their students' (mean age at pretest = 11.51 years; N = 782; 568 language minority and 247 English only) vocabulary knowledge. Using videotaped classroom observations, teachers' speech was transcribed and coded for their total amount of talk, vocabulary usage, and syntactic complexity. Students' vocabulary skills were assessed at the beginning and end of the school year. Results showed variation in students' vocabulary skills and teachers' language use. Hierarchical linear modeling techniques revealed that after controlling for classroom and school composition and students' beginning-of-the-year scores, students' end-of-the-year vocabulary skills were positively related to teachers' use of sophisticated vocabulary and complex syntax, but not teachers' total amount of talk. (Contains 4 tables.)