Here's a plain-language Brief Summary ready to paste - it follows the PRS lay-language style (short sentences, explains the "why," avoids jargon) and fits well within 5,000 characters:

Staying well hydrated helps children stay healthy and concentrate, and it matters most during physical activity. Yet many young children do not drink enough water during physical education (PE) lessons, and some begin the school day already short of fluid.

This study tested whether a short, fun teaching programme could help young children learn about hydration and drink more during PE. The programme used slideshows with simple words, pictures, and short animations, delivered by the children's own teacher for 15 minutes at the start of each PE class, once a week for six weeks.

The study took place in two public primary schools in Sfax, Tunisia, and involved 204 first-grade children aged 6 to 7 years. Twelve classes took part. Whole classes (not individual children) were placed by chance into one of two groups: six classes received the teaching programme, and six classes continued their usual PE with no hydration lessons. Comparing whole classes in this way is called a cluster-randomized trial.

The researchers measured three things each week: how much the children knew about hydration (using a simple yes/no questionnaire), whether they drank water during the PE session, and the small change in each child's body weight across the session, which is an indirect sign of fluid loss. The aim was to see whether learning about hydration in an engaging way actually changes children's drinking behaviour during activity, not just what they know.

Background and rationale. Adequate hydration supports children's health, cognition, and physical performance, yet many children fail to drink enough fluid, particularly during physical education (PE). A prior six-week trial in the same population, using an adapted board game delivered before PE, improved hydration knowledge and behaviour but allocated only eight classes (clusters), which precluded cluster-adjusted modelling. This trial was designed to address that limitation by using a larger number of clusters and a cluster-adjusted analytical framework, while substituting a scalable multimedia format, deliverable with standard classroom equipment, for the physical board game. The intervention was grounded in the Behaviour Change Wheel and its COM-B model (Capability, Opportunity, Motivation-Behaviour), targeting children's hydration knowledge (capability), the social and physical conditions that normalise drinking during PE (opportunity), and willingness to adopt the behaviour (motivation).

Design. This was a cluster-randomized controlled trial conducted in two public primary schools in Sfax, Tunisia, during the 2021-2022 academic year (February to April 2022). The school class served as the unit of randomization (the cluster) and the individual child as the unit of analysis. All eligible first-grade classes in the two schools were enrolled, giving twelve clusters (six per arm) with an average of approximately seventeen children per cluster.

Participants. First-grade children aged 6-7 years were assessed for eligibility. Eligibility required signed parental consent and the ability to participate in all planned data-collection sessions. Children were excluded for exemption from PE on medical or injury grounds, grade repetition, or absence from one or more data-collection sessions. Of 241 children initially assessed, 204 were retained for analysis (101 in the educational arm across six classes; 103 in the control arm across six classes).

Randomization and blinding. Classes were allocated using a computer-generated sequence stratified by school, with three classes per school assigned to each arm. Allocation at the level of the intact class prevented contamination between conditions. Because the intervention was educational, children and teachers could not be blinded; however, outcome assessors and the data analyst remained blinded to allocation, and questionnaires were scored from anonymised, identification-coded forms.

Intervention. The educational arm received six weekly 15-minute multimedia sessions delivered by the regular PE teacher in Arabic, using slideshow presentations combining short written text, static and annotated images, and brief animations, shown immediately before the physical-activity component of PE. Session content progressed from foundational concepts to applied behaviour and contextual factors. Following the educational component, intervention children completed a standard 60-minute PE session identical in structure and duration to the control arm. Control classes continued usual PE with no hydration content and were offered the programme after the trial for ethical equity.

Outcome measurement. Hydration knowledge was assessed with an Arabic adaptation of a validated 22-item awareness questionnaire, scored as a proportion from 0 to 1, administered immediately before the first session and immediately after the sixth. Water consumption during each session was quantified by weighing each child's individually labelled bottle before and after the session, with a recorded value of zero denoting non-drinking. Acute within-session body-mass change, an indirect indicator of hydration status, was computed from calibrated pre- and post-session weighing. Ambient temperature and relative humidity were recorded at each session as covariates.

Statistical analysis. Analyses were performed in Python (statsmodels). Continuous variables were summarised as median (interquartile range) and categorical variables as counts and percentages. Because intact classes were randomized, confirmatory between-group inferences were derived from models accounting for the non-independence of children within classes, using a random intercept for class and, for repeated-measures outcomes, an additional child-level random effect. Hydration knowledge was analysed by mixed-effects analysis of covariance adjusting for baseline score, age, and sex. Water behaviour was modelled as a two-part outcome (the probability of drinking and the volume consumed among those who drank). Body-mass change was modelled with group, session, and their interaction. Intraclass correlation coefficients were estimated for each outcome, and a cluster-level analysis comparing the twelve class means provided a small-sample sensitivity check. Non-parametric tests were used as further sensitivity analyses.

Inclusion Criteria:

• Enrolled in a first-grade class at a participating school
• Signed parental/guardian informed consent
• Able to attend all planned data-collection sessions

Exclusion Criteria:

• Exemption from physical education for medical or injury-related reasons
• Grade repetition
• Absence from one or more data-collection sessions

e-identified individual participant data underlying the published results may be made available to qualified researchers upon reasonable request to the principal investigator, subject to institutional approval and a data-sharing agreement. Data will be available beginning after publication of the main results, with no fixed end date.

Available beginning 6 months after publication of the main results, with no specified end date.

De-identified individual participant data and the supporting documents indicated above will be made available to qualified researchers who provide a methodologically sound proposal. Requests should be directed to the principal investigator and are subject to institutional approval and a signed data-sharing agreement. Approved requesters will receive the data and documents by secure electronic transfer.

Outcome assessors and the data analyst were blinded to group allocation; questionnaires were scored from anonymised, identification-coded forms. Children and teachers could not be blinded given the educational nature of the intervention.