Teacher classroom instructional practice can be a powerful influence on student learning. The Classroom Promotion of Oral Language randomized controlled trial tested whether teacher professional learning focused on promoting oral language in classrooms could improve teacher knowledge and classroom instruction. This study focuses on evaluating the impact of the professional learning on teacher classroom instruction. The nature of classroom talk was used as a means of exploring theories of change and the pathways to practice change. Classroom talk was classified according to its function; organisational, doing, and learning. Teachers from early years classes (first 2 years of school) participated in 4 days of professional learning and received implementation support in their school. Teacher instruction was measured through audio-recordings of classroom talk between teachers and students. The characteristics and proportions of the functions of classroom talk demonstrated by teachers who participated in professional learning (n = 40) and those who did not (n = 38) were compared. Findings indicated no differences in the functions of classroom talk measured with Anstey's type of talk framework following participation in the professional learning; similarities in classroom instruction are discussed and implications for professional learning.