This study investigates how mediated learning designed to improve peer cooperation within activity-based problem solving tasks influences cooperative learning outcomes. Two groups (n = 22) of Year 8 students (mean age 13 +/- 5 months) were randomly assigned to an experimental or control group. The study began with two one-hour sessions of activity-based problem-solving tasks for the control and experimental groups. These sessions were coded for on- and off-task communication. The experimental group then participated in a mediated cooperative learning experience (MCLE) focused on developing cooperative communication and pro-social behaviour. Following the MCLE, a one-hour problem-solving activity session for the collection of data related to on- and off-task communication was conducted for both the control and experimental groups. Results demonstrate that cooperative group on-task communication can be effectively influenced by mediated learning, both intra-group and inter-group, implying that the success associated with cooperative learning may be enhanced by first teaching students how to cooperate. (Contains 5 tables.)