Change representation concerns how changes of text are presented in writing tools. Change representation in collaborative writing can play an important role for the collaborators' understanding of changes of text. We have conducted a laboratory study where 10 pairs of a writer and a reviewer produced argumentative letters by using the change representation functions. We have also set different conditions in the experiental task: (a) two ways of representing changes, indication and display, and (b) two collaboration models, the writer- and the reviewer- initiative models. A primary source of the data was obtained through interviews with the participants. This paper reports their experience of collaboration in writing with change representation tools, relevant design conclusions, and our lessons learned from the study.