STEM (Science, Technology, Engineering, and Math) education is currently receiving much attention from governments and educational institutions. Our work is based on active learning and video-based learning approaches to support STEM education. Here, we aimed to increase student's engagement through reflective processes that embrace video film-making, and subsequent online discussion and evaluation of those videos. We propose a group engagement score that takes into account both individual activity and similarity of participation, thus allowing corrective actions to be taken when unengaged students or groups are identified. We tested these ideas using our own social learning platform that combines the principal features of Social Networks with tools that facilitate collaborative learning design. This platform stimulates students' learning by means of two main reflective processes: participatory production and peer-review. We evaluated this platform and the learning approach it supports in an Object Oriented Programming course and identified interesting differences between group engagement and video ratings. Our principal conclusion is that greater teacher and student awareness of the ongoing activities and group engagement are needed.