As professional learning and development (PLD) for teachers moves online, it is increasingly important to consider what constitutes effective provision. While models of effective PLD abound, online PLD faces challenges to participant engagem ent. In particular, the critical need to build and maintain relationships in professional learning is complicated by the geographic and temporal distribution of online participants as well as the nuances of the technology in use. We argue that online PLD occurs in collaborative text-spaces within learning management systems, social media spaces and their attendant learning objects such as forums. As such, persistent challenges to engagement in online PLD may be met by considering the language-based interpersonal affordances of these text-spaces. We employ a small-scale corpus study and appraisal analysis to demonstrate the value of Systemic Functional Linguistics in addressing the challenges of online learning, particularly how the meaning making resources of the interpersonal metafunction can be used to improve participant engagement.