Recent research by Swain (2000a, 2000b, 1998, 1995), Swain and Lapkin (2001, 1998, 1995) and Kowal and Swain (1997, 1994) has examined the role of collaborative tasks in focusing immersion students' attention on the need for explicit knowledge of grammatical forms and lexical items in the production (especially written) of French texts. This is linked to the importance of output, as well as comprehensible input, in furthering such students' language acquisition. The authors argue that "problems that arise while producing the second language can trigger cognitive processes that are involved in second language learning" (Swain and Lapkin 1995: 371). Kowal and Swain (1994: 75) see collaborative tasks as raising learners' consciousness through the act of talking about the language they are producing and the meaning they are trying to express in producing a text. Swain (2000a) posits that such collaborative tasks can be viewed as a mediating tool for second language learning, involving both a sociocultural and a cognitive process. This paper reports on the findings of an Australian study on collaborative tasks and second language learning. The Canadian research on which the present study was based is briefly described, followed by a description of the data collection. Discussion then focuses on analysis and interpretation of the interactions of pairs of late partial immersion students engaged in a jigsaw task (a cooperative learning group task strategy) in terms of what gaps they notice in their knowledge and how they deal with these. (Contains 1 figure and 2 tables.)