Social interactions are key to promote effective coordination and participation in Computer-Supported Collaborative Learning (CSCL) environments. While current research examines how structural and technological features can enhance collaboration, there is still the need for validated instruments to assess learners’ social Interaction and Online Engagement during online collaborative activities. This study presents an exploratory validation of a scale aimed at assessing learners’ perceptions of social interaction and online engagement after CSCL activities. The scale was piloted within a questionnaire assessing online learning and collaboration, administered in the context of a standard Higher Education course. Data were collected from 68 undergraduate students who completed a synchronous task in the environment of the CSCL tool PyramidApp. The exploratory factor analysis showed three interpretable factors that mediate social interaction in the tool: Cognitive Engagement, Social Engagement and Perception Value of the Experience with satisfactory internal consistency for each subscale. Further research is needed to confirm the factor structure.