Few researchers have examined teachers' perceptions of the inclusion of students with autism spectrum disorders at the high school level. The purpose of this mixed methods sequential explanatory study was to examine teachers' attitudes and perceived needs in teaching high school students with high-functioning autism (HFA). Cognitive constructivism was the theoretical base for this study. Seventy-seven general (GE) and special (SE) education high school teachers completed the Scale of Teachers' Attitudes Toward Inclusive Classrooms. Analysis using an independent samples t test found a statistically significant difference between the teacher groups on the professional issues of inclusion subscale but not on advantages and disadvantages, philosophical issues, or logistics. Spearman rank correlation showed a statistically significant relationship between the amount of teacher training and scores related to the philosophical issues of inclusion but not across the other 3 elements. Five teachers were interviewed about concerns related to including students with HFA. A priori and open coding were used in multiple rounds of interpretive analysis. Teachers expressed the need for flexible interventions, support in finding the least restrictive environment, further training, and opportunities for collaboration. Primary recommendations are: (a) to build opportunities for collaboration between SE and GE into preparation programs and into professional development for teachers and for administrators, and (b) to enhance collaboration with families. Positive social change implications include increased self-efficacy for GE and SE teachers, more consistent implementation of interventions, and more successful inclusion of students with HFA. [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.]