This small study examines how one group (n = 59) of first-year undergraduate students developed their knowledge through co-construction using an online forum as a platform as part of a three-year Initial Teacher Training (ITT) programme. Professional dialogue at the online interface supported them to cope with the challenges they faced during teaching practice. The data showed that there were gains in student subject and pedagogical knowledge, observed to a greater extent among the peripheral learners. The data presented provide an alternative view from that published in the existing literature about the size and type of both peripheral and core online interactions that were useful in building the confidence and competence of students in the role of teachers in a primary classroom. Ultimately, the online knowledge exchange among peripheral participants provided agency in learning over actions and the ability to cope during teaching practice. This was corroborated by student self-assessment using post-online reflective brainstorms. Sixty-four per cent of the students concluded that they would use this new subject and pedagogical knowledge when in school as part of their teaching practice.