Protocol for: Lockable Smartphone Pouches in UK Secondary Schools. A Cohort Study

Introduction Smartphone ownership among UK adolescents is near universal, and teachers report phones increasingly being involved in classroom disruption, with misuse during school hours among the more common serious behavioural issues in secondary schools. Evidence on whether restrictive policies improve behaviour, attainment, or wellbeing remains limited. The primary objective is to assess the impact of a lockable smartphone pouch on educational attainment and behaviour. Secondary objectives are to assess impacts on general functioning, psychological wellbeing, and school-level indicators such as exclusions, and to examine whether effects differ for pupils who may be most at risk. Methods and analysis We will conduct a mixed methods cohort study in secondary schools across Northern Ireland and England during the 2025 to 2026 academic year. The quantitative component uses a serial cross-sectional design, with students completing an online questionnaire at 0, 4, and 8 weeks covering homework completion, classroom disruption, participation in PE and extracurricular activities, peer interaction, and smartphone use. Measures include the Strengths and Difficulties Questionnaire, the Revised Child Anxiety and Depression Scale, the short form of the Smartphone Addiction Scale, and the Bergen Social Media Addiction Scale. Schools will also supply half-termly aggregate data on exclusions, detentions, CAMHS referrals, counsellor visits, and parent visits from September 2023 to May 2026. Assuming 90% power, a two-sided type 1 error of 0.05, an intracluster correlation of 0.02, and 25% loss to follow up, we aim to recruit a minimum of 3,200 students from six or more schools to detect a small effect (Cohen's d = 0.2) on SDQ hyperactivity score. Continuous outcomes will be analysed with linear regression and binary outcomes with logistic regression. Aggregate school data will be analysed using an interrupted time series design. Prespecified subgroup analyses cover SEN or neurodivergent status, area-level deprivation, and existing school phone policy. Qualitative data from focus groups with students and staff and semi-structured interviews with school leads will be analysed thematically using Braun and Clarke's six-phase approach. Ethics and dissemination The study has been approved by the King's College London Research Ethics Committee. A Data Protection Impact Assessment has been agreed with the Northern Ireland Department of Education. Findings will be disseminated through a final report to the Department of Education, peer-reviewed publications, conference presentations, and accessible summaries for participating schools, pupils, parents, and policy makers. Keywords: Smartphone; Schools, Secondary; Adolescent Behavior; Mental Health; Academic Performance