The broad aim of this research was to investigate group work in schools with friends and acquaintances. More specifically, the study sought to identify motivational factors that may underlie students' attitudes and behaviours when working in these contexts. Independent and interdependent self-construal, and self-efficacy for group work, were identified as variables that may be important for working in friendship and acquaintance groups. The participants were Year 10 and Year 11 students from secondary schools in the metropolitan area of Sydney, Australia. Data collection was carried out in three phases, the first two were survey-based, and the third was a mixed-methods study. In phase 1, participants (N = 188) attended two Independent schools. The main data analyses comprised exploratory factor analysis and multiple regression analysis. In phase 2, the participants (N = 583) attended nine randomly selected public schools. Data analysis was carried out using confirmatory factor analysis and structural equation modelling. In phase 3, participants (N = 38), attended two randomly selected public schools. In this phase, survey, observational and interview data were collected and analysed. The observational analysis centred on how students in friendship and acquaintance groups interacted whilst working on a group problem-solving activity. The interviews focused on students' experiences in the group problem-solving activity and their general perceptions, beliefs, and feelings about group work with friends and acquaintances. Group performance in the problem-solving activity was measured. Two results seemed particularly important. First, was the suggestion that self-efficacy for being receptive to the ideas of others and- self-efficacy for group facilitation in the friendship context may "flow-on" to corresponding self-efficacy beliefs in the acquaintance context. Second, interdependent and independent self, and self-efficacy for group work, were identified as important variables with regard to students' attitudes and behaviours in friendship and acquaintance groups. From a theoretical perspective the focus in this research on self-beliefs represents a relatively new way of studying group work with friends and acquaintances. From a practical perspective, the findings from the research should provide direction for teachers when they make decisions about how to organize students into groups for the purposes of learning.