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

Background Smartphone ownership among UK adolescents is near universal. Teachers report phones increasingly being involved in classroom disruption, and misuse during school hours is among the more common serious behavioural issues in secondary schools. Evidence on whether restrictive policies improve behaviour, attainment, or wellbeing remains limited. Objectives 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 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. Students will complete an online questionnaire at 0, 4 weeks, and 8 weeks, covering homework completion, classroom disruption, participation in PE and extracurricular activities, peer interaction during break, and patterns of smartphone use. Measures include the Strengths and Difficulties Questionnaire (SDQ), the Revised Child Anxiety and Depression Scale (RCADS), the short form of the Smartphone Addiction Scale (SAS SV), and the Bergen Social Media Addiction Scale (BSMAS). Each participating school will also supply half termly aggregate data on exclusions, detentions, CAMHS referrals, counsellor visits, and parent visits between September 2023 and 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. Prespecified subgroup analyses cover SEN or neurodivergent status, area level deprivation, and which phone policy is in place at each school. Qualitative analyses comprise focus groups with students and staff at each participating school and semi-structured interviews with school leads. Transcripts will be coded both inductively and deductively and analysed thematically with 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 published in peer reviewed journals and shared with participating schools, parents, and policy makers to inform smartphone policy in schools.