The Open University of Sri Lanka implemented four MOOCs for continuing professional development of practitioners on the adoption of OER and OEP. These CPDMOOCs adopted a scenario-based approach to learning within the social-constructivist pedagogy. Learners in this context were presented with real life situations that engaged them in three inter-connected learning tasks. These were: creation of an artefact as a solution to the challenge they faced in the scenario; sharing of their creations in the discussion forum, and reflecting on the learning process. Engagement in peer-facilitated discussion forum was a key learning activity in each CPDMOOC. This was designed to promote collaborative learning and to facilitate co-construction of knowledge among the learners. This was also an assessment task, where learners were required to share their creations in the discussion forum and provide constructive feedback to each other. This case study investigated how and to what extent, interactions among peers in the discussion forum have supported knowledge construction, in the CPDMOOC on “Understanding OER”. Collection and analysis of data in this qualitative study was guided by the Community of Inquiry (CoI) framework (Garrison, Anderson & Archer, 2001). Critical prerequisites for successful online learning are the promotion of cognitive presence, social presence and teaching presence. An in-depth examination of the online interactions was conducted via content analysis of a total of 430 messages that were posted by 68 participants in 76 threaded discussions using coding and categorizing. The findings indicated active engagement of learners in the discussion forum in different ways according to the three types of presences, which has promoted knowledge construction through peer learning. The presentation will engage the audience in identifying various patterns of peer interactions supporting knowledge construction, and their implications for the design of peer-facilitated discussion forums in CPDMOOCs. // Paper ID 241