Study Aim and Methods (≈250 words) It aims to evaluate the effectiveness, user perceptions, and applicability of the e-CAMP intervention in improving mental well-being and reducing depressive symptoms among adolescents aged 11-15 years. The primary research question is whether e-CAMP can significantly reduce depressive symptoms, measured by the Patient Health Questionnaire-9 (PHQ-9).

Secondary objectives are to examine whether e-CAMP : improves mental health literacy using the Chinese-version Universal Mental Health Literacy Scale for Adolescents (UMHL), promotes healthier smart device use as measured by the Smartphone Addiction Scale (SAS), increases physical activity assessed through the Global Adolescent and Child Physical Activity Questionnaire (GAC-PAQ) , and to evaluate participants' perceptions of the intervention's applicability, acceptability through survey.

A prospective two-arm cluster randomized controlled trial (RCT) following CONSORT 2010 guidelines will be conducted in eight eligible Hong Kong schools, which will be randomly assigned to either the intervention or usual-care group. A process evaluation will also be undertaken.

320 students will be recruited with inclusion criteria : Chinese students aged 11-15 years (Primary 5 to Secondary 2) with parental consent. Students with physical, cognitive, or mental conditions that may affect participation will be excluded.

Students in the intervention group will receive usual school care and access to the e-CAMP mobile app, which they will be encouraged to use at least three times weekly for eight weeks (10-15 minutes per session). Students in the control group will receive usual school care, including a 45-minute nurse-led health talk and PowerPoint handouts.

Mental health during adolescence is a major public health concern with profound long term population health implications. A person's lifelong physical, psychological, and social well-being are established during this crucial developmental period. Estimating that approximately 15% of adolescents aged 10-19 years present with mental disorders, most commonly depression, the World Health Organization (WHO) has identified adolescent mental health promotion as a global public health priority [1]. Adolescent depression is associated with persistent mental health problems, impaired psychosocial functioning, and increased morbidity in adulthood [1-3,5].In Hong Kong, the mental health burden on children and adolescents recently has intensified markedly. During 2020-2024, more than 130 school aged children died by suicide, and the adolescent (age: 10-19) suicide rate reached 7.2 per 100,000 [2,3,8]. Diagnoses of depression, anxiety, and related mental health conditions increased substantially among primary and secondary school students during the 2024/25 school year (vs 2019/20) [2-3]. These alarming trends emphasise the need for effective and preventive population based mental health promotions.

Excessive smart device use is a key modifiable adolescent mental health behavioural risk factor. Empirical evidence links smartphone addiction with sedentary behaviour, unhealthy dietary patterns, and increased depressive symptoms [1,2,4-9,18,35]. Prolonged screen time contribute to established risk factors for physical and mental health problems during adolescence, including physical inactivity and unhealthy lifestyles. Local data indicate that 50.7% of Hong Kong adolescents do not meet the WHO recommendation of ≥60 minutes/day of moderate to vigorous physical activity [2,17,38]; thus, integrated health promotion approaches are needed to address behavioural determinants of mental well-being [1,3,7-9].

Aims: To evaluate the effectiveness, user perception, and applicability of the e CAMP intervention for improving mental well-being and reducing depressive symptoms among young adolescents.

Method: A prospective cluster RCT with two arms according to the cluster CONSORT 2010 checklist and guide [23] will be conducted. Eight eligible schools will be assigned randomly to the intervention or usual care group. The process evaluation will be guided by the RE-AIM framework [19-20].

Significance:

The cluster RCT design combined with implementation evaluation will generate locally relevant evidence to inform future digital mental health promotion strategies in school settings.

At the community and population levels, the project will offer a scalable, cost-effective model combining a mobile health intervention with a standardised school-based health talk, enabling broad school coverage. By evaluating user perception, applicability and sustainability, the study will move beyond efficacy to inform real-world applications.

The findings will provide actionable evidence for schools, healthcare professionals, and policymakers to support early preventive mental health promotion strategies responsive to the needs of Hong Kong adolescents

Inclusion Criteria:

• The inclusion criteria will be students at participating schools who can read Chinese and are aged 11-15 (P5 to F2), with parental consent.

Exclusion Criteria:

• Students with known physical (musculoskeletal) or cognitive/mental problems that would compromise physical exercise or our intervention or outcomes will be excluded.

the plan can be in due course after completion of the study

the researcher who will do the data analysis