For the past two decades, there has been a shift in education to include students with autism spectrum disorder (ASD) in inclusion classrooms. The problem addressed in this study was that the number of pupils with ASD attending mainstream schools is increasing; however, there is a lack of evidence to support whether their needs are being met in the general education classrooms. The purpose of this study was to examine teacher perceptions of their effectiveness in instructing students with ASD, as well as how these perceptions affect their self-efficacy in inclusion classrooms. Gestalt's theory of perception and Bronfenbrenner's ecological theory were used as the theoretical frameworks for this study. There were four research questions used to address the problem and the purpose of this study. This qualitative single case study was conducted in the state of Maryland. The sample size consisted of 15 general education teachers who had a minimum of 5 years of teaching students with ASD in inclusion classrooms in Grades K-5. Due to the COVID-19 pandemic, the traditional method of face-to-face instruction was initially modified to online instruction then later streamlined to include in-person learning in a hybrid model. The data collection methods consisted of semi-structured interviews and teacher observations. Content analysis was used to identify themes from the data collected. The major themes that emerged from the study were teachers' perceptions of their self-efficacy, teachers' needs regarding resources and supports, factors teachers perceive are impacting their success, and barriers that teachers encounter. Results from the study revealed that more than half of the teachers viewed their perceptions of self-efficacy as being confident in their abilities and attributed their skill set to their years of teaching in inclusion classrooms. In addition, teachers shared that they received limited training to instruct students with ASD and needed training and adult support in their classrooms to assist the students during instructions. Recommendations for practice are to provide general education teachers with ongoing training specifically designed to instruct students with ASD and provide adult support in their inclusion classrooms that may result in improved student access to the curriculum. [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.]