ABSTRACTAlthough non-completion is common in community based cognitive skills programmes, little is known about the variables associated with engagement, understanding and dropout from these programmes. In this study, it was hypothesised that personality disorder (PD), learning difficulties and elevated criminogenic need profiles would predict ratings of engagement, understanding and dropout. We did this in three stages. At the pre-programme stage, demographic, risk, personality, learning difficulty and criminogenic need data was obtained for 511 offenders under probation supervision in England, referred to a Thinking Skills Programme (TSP). At the 1 year follow up, all participants’ status as either completer, non- completer or non-starter were distinguished through probation records. For programme starters, facilitator ratings of engagement and understanding were obtained. Findings reported that non-completion was most strongly associated with Antisocial Personality Disorder (ASPD) and a history of self-harm or suicide attempts, which both predicted a three times greater likelihood of dropout. Lower engagement and understanding scores were predicted by difficulties with employment and relationships. Offenders with high levels of antisocial traits, a history of self-harm and elevated dynamic risk profiles show higher attrition rates and make limited progress on community based cognitive skills programmes. Implications for programme delivery and evaluation are discussed.