This paper reports an exploratory study of a Native Speaker Teacher (NST) of Mandarin Chinese and a Primary Languages Teacher (PLT) teaching Chinese to English pre-service primary school teachers, and is particularly focused on the use of target language (TL) by these two co-teachers. Although some studies of TL use have compared the use of target language by native and non-native speakers teaching individually, there are no studies which examine target language use in a native and non-native co-teaching situation, or relate this to the background experience of the teachers. The data collected in this study included observations of planning meetings between both teachers, observations of the teaching of the program, and interviews with both teachers. This paper focuses upon the use of target language by the Chinese Native speaker teacher (NST) and the English Primary Languages Teacher (PLT) and the ways in which this changed and developed across the teaching sessions, as well as the relationship between their TL use, background and beliefs about language teaching in the program. Findings of this study show that, even in a co-teaching situation, target language use by the native speaker teacher and the primary languages teacher differed substantially in terms of their practices of and their beliefs about use of target language, and both were influenced by their own cultures of learning. The results also suggest that working together changed the teaching behavior of both teachers and enabled them to reflect critically on their prior assumptions.