This qualitative dissertation study examined the complex dynamics and structures (i.e., people and/or explicit/implicit classroom-, school-, and district-wide behaviors and practices and school-wide structures) that influence collaboration between teachers of students with disabilities (TOSD) and teaching assistants (TAs). Specifically, I wanted to learn: (1) What are the complex dynamics (i.e., people and/or explicit/implicit classroom-, school-, and district-wide behaviors and practices and school-wide structures) that interact to influence collaboration between teachers and teaching assistants? (1a) What role does each participant stakeholder (i.e., teacher, teaching assistant, and principal) play in those complex dynamics? (1b) How do participants develop their understandings about the roles of TOSD and teaching assistants in the teaching and learning process? and (2) How do participants describe the differences, if any, in collaboration between in-school learning and remote learning? The method of data collection consisted of conducting two rounds of intensive interviews (Charmaz, 2014) with seven participants including three teachers of students with disabilities, three teaching assistants, and one school principal. Participant interview transcripts were analyzed through the theoretical lens of critical bifocality. Four themes emerged from my analysis and findings revealed four complex dynamics that interacted to influence teacher-teaching assistant collaboration: school leaders, school culture, school structures, and the "hidden hierarchy." These complex dynamics were interconnected and worked to shape the school conditions that teachers and teaching assistants worked within. The findings of this study had a number of important practical implications for school leaders and teacher education programs and implications for future research. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]