Communicative approaches to teaching language have emphasized the centrality of oral proficiency in the language acquisition process, but research investigating oral proficiency has been surprisingly limited, yielding an incomplete understanding of spoken language development. This study investigated the development of spoken language at the high school level over five consecutive years, involving more than 1,500 students representing 23 school districts. Quantitative Standards-Based Measure of Proficiency speaking scores and student-produced qualitative spoken samples (n?>?6,000 samples) contributed to an understanding of the development of spoken language. Hierarchical linear modeling (HLM) revealed a consistent growth trajectory of spoken language development, and results indicated that 18-30% of the variance in student outcomes may be attributed to the teacher variable.