Previous research has shown that cognitive bias modification of interpretations (CBM-I) may be a promising intervention for anxiety in youth; however, results are mixed. Given the high comorbidity between anxiety and depression in youth, it is surprising that no child studies have targeted biases associated with both. This study aims to evaluate the effectiveness and acceptability of an online CBM-I intervention (Mindmaster) for children with symptom scores of anxiety or depression above a borderline or clinical threshold. The intervention has been codesigned with children, parents and mental health professionals to promote user engagement.

The study is a randomised controlled trial, with two parallel arms. Participants are 143 children aged 8–10 years with scores of anxiety and/or depressive symptoms above a borderline or clinical threshold. They will be allocated to either the intervention group or the waitlist control group. The intervention consists of 2 weeks of online CBM-I training, with four sessions (10–15 min) per week. Outcome assessments will be conducted at baseline, 4 weeks after baseline (post-training/post-waitlist) and 8 weeks after baseline (follow-up) for the intervention group only. The primary outcome is interpretation bias. Secondary outcomes are anxiety and depressive symptoms and life interference. Analyses will be conducted within an intention-to-treat framework using mixed models for repeated measures.

The study was approved by the University of New South Wales Human Research Ethics Committee (HC220758). Findings will be reported to (1) participating families; (2) presented at scientific conferences and (3) disseminated to peer-review publications. Data will be available from the corresponding author on request.

ACTRN12622001493730.