This study examined the relation between young English language learners' (ELL) native oral language skills and their language input in transitional bilingual education kindergarten classrooms. Spanish-speaking ELLs' ("n" = 101) Spanish expressive language skills were assessed using the memory for sentences and picture vocabulary subtests of the Woodcock Language Proficiency Battery-Revised. Samples of transitional bilingual education teachers' ("n" = 21) speech were recorded and coded for syntactic complexity and vocabulary usage. Results revealed considerable variation in ELLs' language scores, with overall performance below the normative sample. There was also wide variation in teachers' speech across classrooms. Hierarchical linear modeling revealed that gains in ELLs' expressive language skills were positively related to the diversity of teachers' vocabulary and teachers' syntactic complexity. These findings suggest that the quality of teachers' language input, not just the quantity of their input, plays a significant role in the language learning trajectories of ELLs.