This study aimed to increase efficacy for teaching mathematics in pre-service early childhood teachers through the presentation of five video lessons on topics in early childhood mathematics. Each lesson entailed reading a short essay on a topic related to children’s mathematical thinking and then watching a short video of a child engaged in a relevant task and a clinical interview with an adult. This study also examined pre-service teachers’ knowledge of mathematical development (KMD) and intellectual modesty, or the awareness of the limits of one’s knowledge, as possible mediators of change in efficacy. Results showed that the video lessons did significantly increase efficacy for teaching mathematics, but that KMD and intellectual modesty were not significant mediators of the change in efficacy. In effect, confidence appeared disconnected from competence. Follow-up analyses revealed the importance of rich mathematical content within the videos in producing increased confidence and competence.