This paper outlines the types of verbal interactions teachers engage in to challenge children's thinking and problem-solving during cooperative learning. The paper also provides examples of how children model many of the verbal interactions they have seen demonstrated in their discourse with each other. It appears that when teachers are explicit in the types of thinking they want children to engage in, it encourages children to be more focused and explicit in the types of help they provide. Understanding the key role that teachers play in promoting thinking and problem-solving in their students is particularly important given that it is the quality of talk that children generate that is a significant predictor of their learning.