| Teaching assistants (TAs) are tasked with providing effective learning opportunities in introductory laboratory courses that are major contributors to the health of science departments. However, TAs are in a unique position where they often have limited knowledge of pedagogy. Due to the crucial role of TAs, they should be provided with adequate supports to meet instructional goals and promote equity. This research uses mixed methods to analyze four case studies of TAs who were tasked with implementing features of ambitious instruction when provided with educative curriculum materials integrated into a program of professional development. TAs used supports to attend to three types of teacher knowledge: content knowledge, pedagogical knowledge, and pedagogical content knowledge. Supports that fostered TAs to reflect and problematize their practice in productive ways were related to TA learning to align with ambitious instruction. This research has implications for future iterations of TA curriculum materials and professional development. Key Words: ambitious instruction, biology laboratory course, teaching assistant learning, professional development, educative curriculum materials |