Reflection is an important aspect of learning in groups. In collective moments of reflection, learners can share and compare their ideas with others, and by doing so can reach an articulated and personal understanding of a learning task and domain. In the research presented here, e-mail is examined as a means for reflection in the context of group learning. In two design experiments, an e-mail tool is developed that seeks to (1) support collective reflection, and (2) overcome practical problems related to e-mail use in primary classrooms. Two prototypes of the tool are presented and tested in five primary classrooms. We conclude that e-mail supports collective reflection on a learning task after adding the following supportive measures to the regular e-mail program: (1) a fixed partnership, (2) fixed timing, (3) an exercise of individual freewriting, and (4) collective use of a paper worksheet.