The purpose of this study was to identify and analyse specific instances of transactive communication as children engaged in a paired melody writing task using a computer-based composing environment. Transactive communication has been identified as one of the features of general collaborative engagement that is most helpful in an educational sense, and which makes collaborative learning an important tool for learning and teaching. The paper reports the results of an empirical study in which a group of 10 and 11 year olds worked in pairs to compose short melodies using computers. Analysis of between-pupil dialogue suggested that levels of transactive communication varied between pairs, and also within pairs as pupils took on different roles at the computer. Factors of individual difference, such as musical expertise or whether the pair were friends, did not appear to have a significant influence on the extent of, or nature or, transactive communication.