After certification, teachers do not often receive systematic support in their learning and hence mainly depend on informal learning opportunities at work. The present study addresses the question of if and how supervision makes a difference to teacher learning. In a longitudinal mixed-method study, the learning of one teacher is documented in a year in which she had no systematic support but had to adjust herself to an educational innovation. The authors also studied this teacher in a consecutive year in which she did receive individual supervision. During supervision, the teacher became aware of beliefs and patterns that had previously inhibited her from change. This awareness precipitated significant changes in her beliefs and classroom behavior as well as the way she learned. The findings suggest that professional learning will take place only if a teacher is supported in learning how to deal effectively with personal factors involved in the learning process. (Contains 1 table and 1 figure.)