<p>Objective: Despite growing momentum towards personalised mental health care for children and adolescents, a central question remains unresolved: <i>which treatment works best for which child, and under what circumstances?</i> Identifying moderators of differential treatment effects is key to answering this question and guiding clinicians in tailoring interventions for childhood anxiety. However, progress has been hindered by conceptual ambiguity, inconsistent reporting, and methodological limitations in how moderators are defined, tested, and interpreted. This systematic review synthesises research on moderators of cognitive behavioural therapy (CBT) for childhood anxiety, aiming to determine whether any moderators are sufficiently consistent and robust to inform clinical decision-making. Method: A systematic search of the literature delivered records from inception to July 2025. Randomised controlled trials of CBT for youth with anxiety disorders (5—18&#xa0;years) were considered, including studies that reported explicit statistical moderator interactions. Results: Of the 355 full-text articles reviewed, 68 studies originating from 44 randomised controlled trials met the inclusion criteria, reporting 28 significant moderators. Seventeen moderators showed a singular instance of differential treatment effect. The remaining 11 moderators showed multiple instances and were examined in greater detail. Although five moderators showed some evidence for differential treatment effects (age, Social Anxiety diagnosis, baseline anxiety severity, parent psychopathology, and parent acculturation), we cannot conclude that any reliable moderators of childhood anxiety outcome have been identified. Conclusion: This review represents a critical step forward in our search for factors that can guide optimal treatment selection in practice. Although these findings require confirmation through prospective studies, they offer a valuable foundation for precision mental health care. </p>