This study employed a sequential mixed methods explanatory research design to explore the influence of mentoring in the self-efficacy-forming experiences of primary school teachers who participated in a variety of professional development projects on science teaching. In the quantitative phase, survey data drawn from primary school teachers (n = 834) showed that collaborative mentee-mentor activities and metaphorical descriptions of interpersonal relationship were the best predictors of personal science teaching self-efficacy, outcome expectancy, and instructional change. In the qualitative phase, interviews with individual teachers identified their perceptions of how mentoring experiences influenced their development of science teaching self-efficacy and changes they made in their science classrooms. The findings are interpreted through the theoretical lens of the roles of culture and emotions in teacher learning.