This article discusses the quality of professional relationships between educational psychologists (EPs) and other professionals who work around children, young people and their families as part of a multi-agency team (MAT). The perceived barriers to, and facilitators of, effective multi-agency working are explored in relation to their potential impact upon the process of engaging service users in change. The actions that take place within a MAT are analysed from the systemic perspective of sociocultural activity theory (AT), and supported by examples drawn from behaviour and education support teams (BESTs). The implications for professional practice are discussed.