This paper explores how job-embedded professional development supported a Year 1 teacher as he enacted his growing expertise in the teaching of guided reading. By analysing coaching conversations focussed on the teacher's guided reading practices, we studied the way his teaching developed over a 7-month period. Our findings suggest the teacher gained deeper understandings in the domain of reading, which allowed him to be more responsive to children during guided reading. We discuss the factors that enhanced or inhibited his ability to implement what he learned and offer suggestions for supporting teachers through job-embedded professional development.