Few studies have examined how instructor variables relate to student performance measures for individuals with autism spectrum disorder (ASD). The purpose of this study was to examine instructor language and student active engagement in general and special education classrooms for students with ASD. This study included participants (n = 196 students nested within 126 instructors) in the first three years of the Classroom SCERTS Intervention Project, an ongoing randomized controlled trial for elementary students with ASD. Findings documented significant group differences in the categories and the amount of instructor language between general and special education classrooms. Instructors in special education classrooms used significantly more language overall and more language that was directed to individual students, while instructors in general education classrooms used significantly more language during group instruction. Confirmatory factor analysis revealed differences in the structure of instructor language between the classroom settings, with a 3-factor model evidencing the best fit in general education classrooms and a 2-factor model in special education classrooms. Structural equation modeling revealed a moderate, positive association between the instructor Encouraging Interaction and Providing Information factors with student social communication in general education classrooms, and a moderate, negative association between the instructor Facilitative Language factor and student responding in special education classrooms. Additionally, a small, negative association was observed between the amount of language instructors used and student emotional regulation in special education classrooms. This study contributes to a limited body of research on students with ASD in educational settings and provides empirical measures of the language environment in general and special education classrooms. The significant differences in instructor language observed between general and special education classrooms may have important implications for student active engagement in educational settings. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]