Non‐Criminal Justice Interventions for Countering Cognitive and Behavioural Radicalisation Amongst Children and Adolescents: A Systematic Review of Effectiveness and Implementation

Growing numbers of young people are encountering the counter‐terrorism system. This international trend raises important questions about the effectiveness of efforts to prevent and counter childhood and adolescent radicalisation. This review examines the effectiveness and implementation of interventions designed to counter cognitive and behavioural radicalisation amongst children and adolescents up to 19 years of age. It examines secondary and tertiary interventions working with at‐risk and radicalised youth outside the criminal justice system. This focus reflects the growing recognition that diverting young people away from the criminal justice system helps mitigate the risks of securitisation, criminalisation, and stigmatisation. This review sought to answer three research questions: (1) Are secondary and tertiary interventions delivered outside of the criminal justice system effective at countering the cognitive and behavioural radicalisation of children and adolescents? (2) Are secondary and tertiary interventions delivered outside of the criminal justice system being implemented as intended? (3) What factors influence how interventions working with children and adolescents outside of the criminal justice system are implemented? Studies were identified through electronic searches of 20 academic and 50 grey literature sources; hand searches of academic journals and clinical trial repositories; forward and backward citation searches; and consultation with academic experts. Studies published after 2000 in English were eligible for inclusion. Searches of academic and grey literature sources were conducted in August and September 2024, respectively, with all remaining searches completed by December 2024. Studies had to report on secondary or tertiary interventions or prevention work outside of the criminal justice system (i.e., outside of correctional, custodial, or probation contexts) that sought to counter cognitive and behavioural radicalisation, often referred to as countering violent extremism (CVE) programming. Three types of interventions were included: (1) those designed for children and adolescents; (2) those working with children and adolescents as part of wider cohorts, provided a significant proportion of clients were aged 19 or under, or that provided insights specific to children and adolescents; or (3) those working with youth (or young people), broadly defined. Experimental or stronger quasi‐experimental research designs were eligible for inclusion in the assessment of effectiveness (Objective I). Inclusion criteria for the assessment of implementation (Objective II) and of implementation factors (Objective III) were broader, and included non‐experimental quantitative designs and qualitative research. The corpus of evidence was screened by trained reviewers, guided by screening tools, across a title/abstract and full‐text screening phase. Data were extracted using a piloted tool to capture key information on each included study. Risk of bias information was extracted using relevant existing tools. Effectiveness data from a single study was converted into a standardised effect size. Data relating to implementation was coded through a process of inductive and deductive coding. Twenty‐nine studies were included in the review. Only one quasi‐experimental study was eligible for inclusion in the analysis of effectiveness (Objective I). In this study, Kolbe (2019) reported that at‐risk young people participating in a group‐based intervention who also received individualised home‐based support were less likely to join a violent extremist group than young people who only participated in the group‐based intervention (Chi‐square: 5.295, df = 1, p = 0.021). This represents a large effect (Odds ratio: 0.181, 95% CI [0.0366, 0.8963]). However, the fact that this study was assessed as having a serious risk of bias, coupled with the lack of other eligible research designs, means there was insufficient evidence to draw conclusions about effectiveness. Evidence relating to implementation was drawn from qualitative and mixed‐methods studiesassessed as moderate to high quality. Seven studies examined how interventions were implemented (Objective II), including whether they were implemented as intended, or had been able to reach eligible clients. These studies reported positive results, but highlighted challenges that interventions might face in reaching those most in need of support (i.e., those most ‘at risk’), and the need for interventions to be flexible and adapt their approach when needed. Twenty‐eight studies examined implementation factors, and twenty‐seven analysed moderators (Objective III). Three types of implementation factors were identified: (1) Structural and systemic factors (e.g., knowledge and expertise, multi‐agency and partnership working); (2) Identifying and engaging eligible clients; and (3) Working with clients (e.g., relational processes; client‐centred approach). The moderators were the national and local context, client characteristics, and delivery contexts. The review found very little research that speaks to the effectiveness of interventions working with youth outside the criminal justice system. The absence of such research does not mean that current interventions should be considered ineffective, nor that a criminal justice response is likely to be more effective. It is also important to recognise that previous research has found that the evidence base underpinning these interventions is evolving, and that stronger non‐experimental research designs are being used to analyse effectiveness. However, in common with the wider evidence base on secondary and tertiary interventions – including those delivered through the criminal justice system – current knowledge remains limited. The field has developed a better understanding of the factors that facilitate or create barriers to implementation. Research on implementation offers a solid foundation from which to develop a more evidence‐based approach to policy and practice and provides several avenues for future research. The most obvious implication for policy and practice is to build evaluation into programme design. Notwithstanding the challenges to evaluating secondary and tertiary interventions, this effort should prioritise the use of stronger methodological designs that make it possible to demonstrate programme effectiveness. Further implications for policymakers and practitioners to consider include promoting a non‐stigmatising youth‐centred approach; applying a holistic and multidisciplinary social‐ecological approach; developing systems and structures that support practitioners and young people; recognising the importance of relational processes that enable systems and structures to work effectively; and active and ongoing engagement with families.