ABSTRACT Background: Peer Group Supervision (PGS) is based on the belief that there are no intended power relationships as the members of PGS are generally of equal status and they rotate roles and decide how PGS will be structured (Inskipp, 1996). The planned PGS meetings are leaderless, egalitarian in principle and comprise of practitioners who work in similar fields (Kadushin & Harkness, 2002). PGS members can draw upon each otherÃ¢Â€Â™s experiences, gain advice on difficult cases and issues (Askhurst & Kelly, 2006; Davys & Beddoe, 2010; Kaiser & Barrettta-Herman, 1999) and develop a wide range of skill-based knowledge (Proctor, 2010). PGS has been found to be an effective form of peer support to a wide range of professionals. Limited research exists regarding PGS within an Educational Psychology Service (EPS) context. The aim of this research study is to employ a Realistic Evaluation (RE) framework to evaluate PGS within an EPS. Participants: An EPS provided the context of the research study. The sample of participants reflected the composition of the EPS: four full-time equivalent main grade Educational Psychologists (EPs), one main grade EP 0.4, one Senior EP and the Principal Educational Psychologist (PEP). All participants were actively sought and recruited through purposive sampling (Thomas, 2009). Methods: I adopted a RE framework (Pawson & Tilley, 1997) as the methodological approach. RE is a theory-driven approach to evaluate social programmes (Pawson & Tilley, 1997). RE aims to identify causal mechanisms and the conditions under which they are activated to produce specific outcomes. The realist formula is symbolised as Context (C) + Mechanism (M) = Outcome (O), (CMO). Semi-structured interviews and a focus group were the main means of collecting the qualitative data. Thematic analysis coding described by Braun & Clarke, (2006) was used to analyse the data. Analysis/Findings: Semi-structured interviews and a focus group were thematically analysed following full transcription (Braun and Clarke, 2006). Global themes were organised and structured under a realist CMO formula. Based on the methodology employed, the findings reveal contextual and mechanism themes to support the use of PGS within an EPS. The key mechanisms within PGS were: team dynamics, commitment and protected time. The key contexts were: social conditions, the PGS model and structure. The key outcomes were coded into educative, supportive and managerial (self-monitoring) functions (Hawkins & Shohet, 2006). EPs reported that PGS was valued, it had a sense of purpose and overall it provided a forum to foster positive engagement and affinity with peers (Marks & Hixon, 1986; Christensen & Kline, 2001). PGS was highlighted as organic because other EPS interest/research groups developed plus there was a growing interest from schools and other settings in PGS led by EPs. One disenabling mechanism noted to be hampering the implementation of PGS included EPs contending with competing priorities such as, extra workload and time pressures. This resulted in EPs missing PGS sessions. Conclusion/Implications: This thesis contributes to the limited amount of literature on the study of PGS within the field of educational psychology. This study gives a greater insight into the use of PGS within an EPS context. PGS has become embedded into policy and practice within the EPS. Additionally, as other teams and school practitioners have become aware of PGS, the demand for PGS training has increased and has become part of the traded elements of the psychological service delivery.