Research shows correlations between children's problematic behaviours and reduced academic performance, stressed teacher-child relationships, poorer peer interactions, higher involvement in deviant behaviours, lower school adjustment, and increased chances of dropping out of school. Problematic behaviour is a source of stress for teachers and predictive of teacher burnout. The Incredible Years (IY) Teacher Classroom Management (TCM) Programme is one intervention developed to address problematic behaviours via training teachers to use positive and proactive management strategies. Ultimately, by changing teachers' classroom management strategies, the programme aims to affect children's behaviours. This systematic review utilises advanced statistical analyses and cross-synthesises evidence from both quantitative trials and qualitative studies to answer the research question: What is known about the effectiveness of the Incredible Years Teacher Classroom Management (IY TCM) Programme and how do people experience/perceive the programme and its effects? This review searched electronic databases, websites related to the IY Series, and reference lists of included studies. Fourteen records were included in this review and jointly described nine studies that fit into the quantitative, qualitative, or both sections of this paper. The nine included studies took place across five different countries: one study in England and two studies each in Ireland, Jamaica, the United States, and Wales. Decisions about which programmes to implement in schools are based on a variety of factors, including effectiveness of a given programme and how acceptable/appropriate it is for the context. By systematically reviewing effectiveness trial evidence alongside data on stakeholders' experiences with the IY TCM Programme, and then cross-synthesising the findings from both strands, this study provides the most comprehensive picture for both decision-makers and researchers in understanding if the IY TCM Programme benefited children and teachers and the processes of how people experience it. [SREE documents are structured abstracts of SREE conference symposium, panel, and paper or poster submissions.]