This randomized controlled trial evaluates whether a 12-week school-based physical education program that combines cooperative sports games and ball sports can improve mental health and physical fitness in rural left-behind children. Left-behind children are those who remain in rural areas while one or both parents migrate for work. These children may experience social and emotional challenges in addition to physical health concerns.

Forty sixth-grade boarding students who met the criteria for left-behind children were randomly assigned to either a mixed training group or a usual physical education control group. The intervention was delivered during regular school physical education classes three times per week, 90 minutes per session, for 12 weeks. Each session included cooperative physical games designed to promote peer interaction, followed by structured soccer or basketball training activities.

Mental health was assessed using the Mental Health Test (MHT), and physical fitness was evaluated using standardized school-based tests including lung function, running performance, flexibility, and coordination. Outcomes were measured before and after the intervention.

The study aims to determine whether optimizing the structure of routine school physical education can provide a feasible and scalable strategy to support both psychological well-being and physical development in vulnerable child populations.

This study is a single-center, parallel-group randomized controlled trial conducted in a rural primary boarding school in China. The objective was to evaluate the effects of a structured 12-week mixed physical education intervention integrating cooperative sports games and ball sports on mental health and physical fitness in left-behind children.

Eligible participants were sixth-grade students who had been separated from one or both parents for more than six months and met the study's screening criteria for left-behind children. After baseline assessment, participants were randomly allocated in a 1:1 ratio to either the mixed training group (MTG) or the control group (CONG) using block randomization (block size = 4) with allocation concealment via sequentially numbered opaque sealed envelopes. Outcome assessors were blinded to group assignment.

The intervention was delivered within the routine physical education curriculum (three sessions per week, 90 minutes per session, for 12 weeks). Each session included: (1) a 20-25 minute cooperative game segment emphasizing social interaction and group participation; (2) a 55-60 minute structured soccer or basketball training segment with progressive skill development and small-sided games; and (3) a brief cool-down period. Exercise intensity was staged using target heart rate zones corresponding to approximately 60-85% of age-predicted maximal heart rate.

The primary outcome measure was the total score of the Mental Health Test (MHT). Secondary outcomes included MHT subscales and standardized physical fitness indicators (vital capacity, 50-m dash, 8×50-m shuttle run, rope skipping, sit-ups, sit-and-reach, and body mass index). All outcomes were assessed at baseline and immediately post-intervention.

Data were analyzed using two-way repeated-measures analysis of variance to assess group, time, and interaction effects. The study was conducted in accordance with the Declaration of Helsinki and was approved by the institutional ethics committee.

Inclusion Criteria:

• Aged 12 to 13 years
• Enrolled in the sixth grade of the participating rural primary school
• Classified as left-behind children, defined as separation from one or both parents for more than six months due to parental migration for work
• Boarding-school students during the study period
• Provided written informed consent from legal guardians and written assent from the child

Exclusion Criteria:

• Children from single-parent families or orphans
• Presence of physical, neurological, or medical conditions that would limit participation in regular physical activity
• Participation in any structured extracurricular physical training program during the study period

Outcome assessors responsible for physical fitness testing were blinded to group allocation. Participants and the physical education teacher delivering the intervention were not blinded due to the nature of the study design.