As part of our longitudinal study of TESOL instructors' engagement with peer-reviewed journal articles in professional reading groups, we examined the processes involved in knowledge co-construction in three group discussions. Audio-recordings of the discussions were analysed using process coding to identify the quality and quantity of the group members' (n = 18) contributions and the processes of knowledge co-construction. Findings revealed that the group members' contributions were characterized by 16 different language functions. The most commonly used functions, agreeing, elaborating and sharing experiences, strengthened group rapport and promoted a positive learning environment. All 16 language functions contributed to the processes of introducing, developing, crystallizing, combining, and creating knowledge that stimulated innovative evidence-informed practices. An awareness of the processes of knowledge-co-construction and their potential to address professional learning and development needs may encourage teachers to engage in autonomous reading groups and support them in the creation of innovative next practices.