Supporting children’s reflection-in-action during Design-based Learning (DBL) processes can help them to make sense of their design activities and optimize their action on the spot. Earlier work has not examined the process in a way to inform the public on detailed design decisions for scaffolding. In addition, the social character of reflection-in-action is underappreciated in previous work. In this paper, we begin with building a conceptual framework. We identify four elements that define reflection-in-action: surprising event, knowing-in-action, improvisation to respond to surprise, effects on ongoing action. We describe a qualitative study that examined how these elements manifested themselves during a collaborative DBL workshop with 9 children. Our study uncovered six types of reflective discourses and shows how these on-the-spot reflections can affect subsequent group behaviors. Based on our results, we discuss the social process of reflection-in-action, the problems revealed and the requirements to design technological reflection scaffolds in a collaborative DBL context.