Given the rising prevalence rates of autism spectrum disorders (ASD), schools are serving an increasing number of students with ASD (Scull & Winkler, 2011). Researchers have highlighted active engagement as a critical component of effective interventions for students with ASD (National Research Council, 2001), yet there is limited research related to engagement in school-age children with ASD. Joint engagement, which reflects the social nature of engagement, is a known area of deficit in young children with ASD (Adamson, Bakeman, Deckner, & Romski, 2009) and may be an ideal construct for assessing the engagement of older students with ASD in the classroom. This descriptive study was designed to examine the relationship of joint engagement with classroom ecological factors and student characteristics. The sample included 25 elementary and middle school students with ASD served in eight self-contained special education classrooms across three different school districts. Joint engagement was measured during typical classroom instruction in individual, small group, and large group sessions using live coding procedures. Data for the independent variables included the classroom ecological factors of group size, teachers' use of student directed practices, teacher interaction style and teacher report of burnout, and the student characteristics of autism severity, expressive communication, and receptive vocabulary. Mixed level modeling was used to examine relationships between joint engagement and the independent variables. Joint engagement was significantly related to group size, teachers' use of student-directed practices, students' autism severity, and students' expressive communication skills. There were no significant relationships of joint engagement with teacher interaction styles, teacher report of burnout, and students' receptive vocabulary skills. Additionally, the consistency of joint engagement as measured by within student variance was 38%, 66%, and 82% for large group, small group, and individual contexts, respectively. These findings have important implications for educational policies and practices and future research related to active engagement and effective interventions for students with ASD. [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.]