This study will use a multistage cluster randomized controlled trial (RCT) design. All cities in Guangdong Province will be divided into 2 economic strata. The 2 cities with the highest prevalence of overweight or obesity will be selected from each stratum. Schools within these cities will be randomly assigned to either the intervention group or the control group. The intervention group will receive enhanced family-based educational interventions, while the control group will continue with regular practices. The study will involve baseline data collection, 4 rounds of interventions, and follow-up assessments over 12 months. Figure 1 shows the flowchart of the study design.

The study will be conducted in Guangdong Province, which includes 21 prefecture-level cities. Within these cities, a total of 40 schools (including primary, middle, and high schools) will be selected based on their participation in an initiative called Surveillance for Common Disease and Health Risk Factors Among Students in Guangdong Province. The selected schools will represent a diverse socioeconomic and demographic student population to ensure the generalizability of the study findings. The intervention will be implemented in both urban and rural settings to capture the varying dynamics of childhood and adolescent obesity across different environments.

Stratified randomization will be used, considering the comparability between the intervention and control groups. First, all cities in Guangdong Province will be divided into 2 economic strata. The 2 cities with the highest prevalence of overweight or obesity will be selected from each stratum. Second, schools will be stratified according to school types, with 4 primary schools, 4 middle schools, and 2 high schools being selected in each city. Subsequently, the selected schools within each stratum will be randomly assigned in a 1:1 ratio to either the intervention or control group. To ensure rigorous allocation concealment, a random allocation sequence will be generated by an independent statistician blinded to the participating schools. Opaque, sealed envelopes containing group assignments will be prepared by staff not involved in intervention implementation, and allocations will be disclosed only after completion of school enrollment.

Participants in this study will be school-aged children and adolescents from Guangdong Province who meet the following criteria: aged between 8 and 17 years and enrolled in grades 4 and 5 (primary school), grades 7 and 8 (middle school), and grades 10 and 11 (high school). They must be identified as overweight or obese based on the Screening for Overweight and Obesity Among School-Age Children and Adolescents (WS/T 586‐2018) standards during the baseline assessment. Additionally, both students and their parents or guardians must provide informed consent to participate in the study.

Participants will be excluded if they meet any of the following criteria: refusal by students or their parents or guardians to participate in the study; presence of mental health conditions, intellectual disabilities, or other factors that may impede understanding or cooperation with the study procedures; and presence of severe illnesses or undergoing major medical treatments, such as dialysis or chemotherapy, which may affect the study outcomes.

Assuming an effect size (Cohen d) of 0.1, an SD of 0.05, a significance level (α) of .05, and a power (1-β) of .9, with an intracluster correlation coefficient of 0.01, an average cluster size (m) of 160 students, and an overweight and obesity prevalence rate of 20%, the required sample size n for each cluster (school) was calculated using the following Cohen d formula:

Considering that the sample size for a cluster RCT needs to be adjusted based on the intracluster correlation coefficient, the adjusted sample size n was calculated. By multiplying the adjusted sample size n by the number of clusters (schools), the total sample size was estimated to be 539 students. Accounting for a 20% dropout rate, the total sample size required is approximately 674 students.

The intervention group will receive an enhanced family-based educational intervention in addition to the regular prevention measures implemented by schools. Each student and their parents will receive 1 health report (Multimedia Appendix 1) and 4 sets of educational materials, which will be developed by the Guangdong Provincial Center for Disease Control and Prevention and delivered by schools. Each set includes an enhanced health education booklet, a family weight management action guideline, and an advocacy letter (Multimedia Appendix 2). Details of these intervention components are shown in Table 1. Participants in the control group will only receive the regular prevention measures implemented by their schools. These measures may include routine physical examinations, general health education activities, and school-based physical activity programs, but no additional educational materials or personalized health reports will be provided to the control group.

Primary outcomes are the changes in BMI and standardized BMI (zBMI) over a 12-month period. These outcomes will provide a direct measure of the intervention’s effectiveness in reducing overweight and obesity among the participants. The change in BMI will be assessed from baseline to the end of the study, while the change in zBMI will account for age and sex differences, offering a more nuanced understanding of the weight status changes in the school-aged children and adolescents.

Secondary outcomes include the incidence and recovery rates of both general and central obesity; changes in standardized waist-to-height ratio (zWHtR) and standardized waist circumference (zWC); and changes in parental knowledge, attitude, and practice (KAP) scores (Multimedia Appendix 3) [33]. Specifically, the incidence of general obesity will be determined by newly diagnosed students with obesity at the end of the study among participants who are not obese at baseline, and the recovery rate will be calculated based on the number of students who transition from obesity to nonobesity status. Similarly, the incidence and recovery rates of central obesity will be assessed. Additional secondary outcomes involve changes in zWHtR and zWC over 12 months. The staff who measure the children’s weight and height will be blinded to the school allocation. Furthermore, KAP scores will be assessed at the start of the intervention and at 3, 6, 9, and 12 months after the intervention to gauge improvements in health literacy regarding childhood and adolescent overweight and obesity. These comprehensive outcomes will help elucidate the effectiveness of the enhanced family-based educational interventions and their impact on health behaviors and literacy.

Process evaluation will be used to evaluate the feasibility and acceptability of the trial by assessing parental compliance. Specifically, parent questionnaires (Multimedia Appendix 4) are administered at 3, 6, 9, and 12 months after the intervention to evaluate adherence to dietary and physical activity recommendations.

Data collection will include both questionnaire surveys and anthropometric measurements, carried out at the beginning and end of the study. The 2024 Student Health Status and Influencing Factors Survey, integrated with the provincial Surveillance for Common Disease and Health Risk Factors Among Students project, will be administered before the study begins and after it concludes. Both students and their parents will complete the survey, which is provided by national authorities and includes versions for primary and secondary school students. The survey covers general demographic characteristics, dietary habits, physical activity, smoking and drinking behaviors, use of eyes outside of school, electronic screen use, outdoor activities, and sleep habits. Additionally, parental KAP questionnaires for the intervention group will be collected at baseline and 3, 6, 9, and 12 months, while those for the control group will be obtained at baseline and after 12 months. Nutritional status monitoring will include measurements of height, weight, and waist circumference following standardized procedures with light clothing and without shoes. BMI will be calculated as weight in kilograms divided by height in meters squared (kg/m²). Waist circumference will be measured horizontally at the midpoint between the last rib and the top of the iliac crest. General obesity will be determined by sex- and age-specific BMI cutoff values according to the Screening Standard for Overweight and Obesity Among School-Age Children and Adolescents (WS/T 586-2018). Central obesity will be based on the 90th percentile of waist circumference by sex and age according to the High Waist Circumference Screening Threshold for Children and Adolescents Aged 7-18 Years (WS/T 611-2018). Data collected from paper-based questionnaires will be independently double-entered by 2 trained university students and subsequently entered into an electronic database.

The collected data will be analyzed to evaluate the effectiveness of the enhanced family-based educational interventions. Descriptive statistics will summarize baseline characteristics of the intervention and control groups, with means (SDs) or medians (IQRs) for continuous variables and frequencies (percentages) for categorical variables. Comparisons between groups will be made using independent sample 2-tailed t tests or Wilcoxon rank-sum tests for continuous variables and chi-square tests or Fisher exact tests for categorical variables. Multivariable regression analyses will adjust for potential confounders and assess the intervention’s independent effects on primary and secondary outcomes, including changes in BMI, zBMI, zWHtR, and zWC over 12 months. Parental KAP scores will be the sum of scores in each questionnaire entry, which will be scored on a scale of 1 to 4 depending on the option. KAP scores from the intervention group will be assessed every 3 months, and the difference between KAP scores at the start and the end of the study will be used to evaluate changes in health literacy.

To address the handling of missing data in our study, we will use a combination of intention-to-treat, per-protocol, and complete case analyses. The intention-to-treat analysis will include all participants as randomized to account for nonadherence and dropouts, thereby preserving the randomization’s integrity. The per-protocol analysis will focus on participants who complete the intervention according to the study protocol, offering insights into the efficacy under ideal adherence. Additionally, we will conduct a complete case analysis, which considers only those participants with complete data on all variables of interest. This approach will allow us to maintain the rigor of our statistical evaluation while acknowledging the limitations associated with missing data.

This study protocol was reviewed and approved by the institutional review board of the School of Public Health, Sun Yat-sen University (approval number 2024-160). Informed consent will be obtained from all participants and their parents or guardians prior to enrollment in the study. All procedures will be conducted in accordance with the ethical standards of the responsible committee and the World Medical Association Declaration of Helsinki. Participant confidentiality will be ensured by assigning unique study IDs, and privacy will be strictly protected. Any participant who experiences harm related to trial participation will receive appropriate medical care and compensation.

The enhanced family-based educational intervention described here is anticipated to be effective for obesity control, reducing the prevalence of overweight and obesity among children and adolescents in Guangdong Province. We hypothesize that, compared with the control group, the intervention group will show significantly more favorable changes in BMI, zBMI, zWHtR, and zWC over the 12-month period. We also anticipate a significantly lower incidence of general obesity and a higher recovery rate in the intervention group. Furthermore, the intervention is expected to improve parental health literacy. This study integrates surveillance feedback with an enhanced family-based educational intervention, aiming to generate critical evidence to inform obesity prevention and control policies in China.

Previous intervention studies with family involvement have been predominantly conducted in single, high-income cities [28-32], limiting the generalizability of their findings to populations with different economic levels in China. Furthermore, these studies overlooked standardized family guidelines and the timely feedback of surveillance results to parents [34], neglecting elements essential for sustained engagement. To address these gaps, this study uses a multicity cluster RCT design across cities of varying economic levels. Additionally, we will provide structured educational materials, including the actionable “Three 1/2s” initiatives and child health reports for parents, aiming to facilitate practical implementation and enhance family engagement.

This study has some strengths, including randomly selecting 4 cities from 2 economic strata to enhance representativeness. Additionally, schools will serve as the unit of intervention, rather than individuals, to minimize contamination between groups and improve implementation feasibility. Several limitations should be acknowledged. First, although a relatively short follow-up period may limit the detection of significant intervention effects on the control of overweight or obesity, we implemented 4 rounds of enhanced intervention, with continuous process evaluations and monitoring of parental health literacy. Second, although the study protocol does not include tailored, culturally adaptive materials, analyzing the data for differential effects across socioeconomic subgroups may provide insights to inform future refinements of intervention strategies. Finally, the anthropometric measurements will be performed only at baseline and at the end of the study based on the provincial Surveillance for Common Disease and Health Risk Factors Among Students project. The 2-point measurements restrict our ability to capture the dynamic trajectories of nutritional status during the study. Future studies incorporating more detailed and frequent measurements are warranted to better characterize the temporal trajectories of the intervention effects.

This study aims to assess the effectiveness of a cost-effective family-based educational intervention to address childhood obesity in China. If proven effective, this framework could provide a scalable solution for nationwide implementation. Future research may explore tailored strategies across diverse socioeconomic and urban-rural contexts to enhance intervention effectiveness. In addition, identifying the optimal frequency of parental reporting would be valuable for maximizing long-term adherence.

Study results will be published in peer-reviewed journals and presented at conferences and relevant stakeholder engagement activities. No information that can identify participants will be included in any publication. Participants who explicitly express a wish to be informed about the study outcome will be contacted and provided with an article or poster containing a lay summary of findings.

This cluster RCT will evaluate the effectiveness of an enhanced family-based educational intervention in children and adolescents with overweight or obesity. By integrating parental reporting into the existing provincial health surveillance system, the study aims to bridge the critical gap between school-based screening and family-based management, addressing widespread underrecognition of childhood obesity. The findings will provide evidence on the efficacy and feasibility of this scalable, family-based model. If proven effective, this approach could be incorporated into national surveillance programs, offering a sustainable public health strategy to curb the growing obesity epidemic.