This study explores what the microgenetic method can tell us about the way emotions change during computer-supported collaboration. It is applied to analyse fluctuations in three components of the challenge experience in a collaborative game: individuals' feelings of challenge, the similarity of these feelings with those of a partner, and their awareness of a partner's feelings of challenge. In four sessions over two weeks, observations were collected of collaborators' emotions and their understanding of a partner's emotions at various points within each session. Individuals' feelings showed substantial and frequent fluctuations within each session but not across sessions. Collaborative partners showed much similarity and synchrony throughout as well as accurate awareness of their partner's emotion. We conclude by discussing why these findings are important for computer-supported collaboration, and difficult to observe with approaches other than the microgenetic method.