Background: Collaborative learning is recognized as an effective learning tool in the classroom. In order to optimize the collaborative learning experience for children within a collaborative partnership, it is important to understand how to match the children by ability level, and whether assigning roles within these dyads is beneficial or not. Aims: The current study investigated the effect of partnering children with different task-specific abilities and assigning or not assigning helping roles within the dyads on the quality of talk used in a collaborative learning task. Sample: The participants in this study comprised 54 year 6 pupils from a Western Sydney government primary school (boys=26, girls=28). The ages ranged from 10 years 10 months to 12 years 4 months with a mean age of 11 years 4 months. Method: The children were formed into 27 single sex dyads of low-middle- and low-high-ability partnerships. In half of each of these dyads the higher ability partner was asked to help the lower ability partner, which was compared with just asking partners to work together. The quality of talk used by the dyads while working collaboratively on the problem-solving task was analysed using a language analysis framework developed by Mercer and colleagues (e.g. Littleton "et al.", 2005; Mercer, 1994, 1996). Results: Results of this study found that children who worked collaboratively in the low-middle-ability dyad condition demonstrated significantly more high-quality exploratory talk than those in the low-high-ability dyad condition. Although there was no significant difference between dyads who were assigned roles and those who were asked to work together, there was an interaction trend which suggests that low-high-ability dyads, who were given the roles of helper and learner, showed more exploratory talk than dyads who were asked just to work together. Conclusion: Mercer's re-conceptualization of Vygotsky's Zone of Proximal Development (ZPD) in terms of the Intermental Development Zone (IDZ), which is reliant on constructive challenging discourse, can potentially provide a platform upon which all learners in the classroom can benefit from collaborative learning experiences.