Under most circumstances school students learn in social contexts. Recently, there has been growing interest in the role of friendship in student learning and cognitive development. This chapter focuses specifically on friendship and acquaintance groups and the development of school students' collaborative learning skills. We begin by considering the importance that educational systems across the globe now place on collaborative learning skills and current educational interventions designed to improve these skills. We then examine claims put forward by some writers about friendship relations, which suggesl that friendship groups provide a unique and favorable context for the development of students' capabilities as effective co-learners. This will include assessing the extent to which these claims are supported by empirical evidence. We then present some results from our own research, based on Social Cognitive Theory, which looks at students' self-efficacy beliefs for their group process skills in friendship and acquaintance groups. The focus on group processes represents an important step forward in research on self-efficacy and group Jearning, because research in this area has largely focused on content aspects of group learning ralher than lhe process aspects. Of particular note, we discuss empirical findings, which suggest that students' self-efficacy beliefs about their group process skills developed in the friendship context may transfer to some extent to the acquaintance context. In addition, we outline a number of potentially important directions for research in this area. Practical advice for teachers and scholars interested in friendship relations and collaborative learning is shared.