Learning Assistants (LAs) are undergraduate students who have previously succeeded in a course and return to assist faculty in engaging current students. The authors used a mixed methods approach to explore changes in LAs' teaching self-efficacy and pedagogical knowledge (PK) over a semester. They found that LAs significantly improved their teaching self-efficacy and PK. Qualitative data revealed that LAs became more confident about engaging meaningfully with students and that their pedagogical approaches aligned more with active learning. The authors provide suggestions for instructors to leverage LAs' confidence and pedagogical understanding.