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Abstract
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Before
This study is based on a randomized controlled trial conducted in approximately 20 fourth-grade classes across ten different schools in France. It has two main objectives: 1) To investigate the existence of peer effects on food preferences and behaviors; 2) To test the impact of a message promoting fruit and vegetable consumption, varying by source (either a peer or a teacher) and content (health-related vs. environmentally oriented), on the pupils' knowledge and eating behaviors in the school canteen. Food preferences, individual characteristics, and dietary practices will be assessed for both children and their parents in order to perform heterogeneity analyses.
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After
This study is based on a randomized controlled trial conducted in approximately 20 fourth-grade classes across ten different schools in France. It has two main objectives: 1) To investigate the existence of peer effects on food preferences and behaviors; 2) To test the impact of a message promoting fruit and vegetable consumption, varying by source (either a peer or a teacher), on the pupils' knowledge and eating behaviors in the school canteen. Food preferences, individual characteristics, and dietary practices will be assessed for both children and their parents in order to perform heterogeneity analyses.
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Last Published
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Before
October 21, 2025 10:42 AM
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After
December 18, 2025 09:53 AM
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Intervention (Public)
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Before
The intervention is based on the delivery of a food-related message addressing either health or sustainability.
The delivered message consists of a short text that is read aloud, followed by the day's school canteen menu.
The short texts were developed based on focus groups with 4th-grade pupils, during which food practices, health, and sustainability were discussed.
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After
The intervention is based on the delivery of a food-related message addressing health.
The delivered message consists of a short text that is read aloud, followed by the day's school canteen menu.
The short text was developed based on focus groups with 4th-grade pupils, during which food practices, and health were discussed.
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Intervention Start Date
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Before
January 12, 2026
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After
January 19, 2026
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Intervention End Date
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Before
January 30, 2026
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After
February 09, 2026
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Primary Outcomes (Explanation)
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Before
One label with each participating child's anonymous number will be affixed to the tray for the day. At the beginning of the meal, a research assistant will launch an app using AI that allows taking a photo of each participating child's tray, before they eat. A photo of the tray will be taken again at the end of the meal. The data will then be transcribed into an Excel file, indicating the quantity variation of each food item on the tray before and after the meal. A dedicated AI app will be used to estimate quantity variations.
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After
One label with each participating child's anonymous number will be affixed to the tray for the day. At the beginning of the meal, a research assistant will launch an app using AI that allows taking a photo of each participating child's tray, before they eat. A photo of the tray will be taken again at the end of the meal. The data will then be transcribed into an Excel file, indicating the quantity variation of each food item on the tray before and after the meal. A dedicated AI app will be used to estimate quantity variations of each food item of the tray.
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Randomization Method
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Before
Two schools were randomized into each treatment group, ensuring that no two schools within the same group were located in the same district. Furthermore, each group included one school from a low socioeconomic background and one from a high socioeconomic background. Randomization was performed in the office using a computer-based procedure.
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After
Two to three schools were randomized into each treatment group, ensuring that none of them within the same group were located in the same district. Furthermore, each group included one school from a low socioeconomic background and one from a higher socioeconomic background. Randomization was performed in the office using a computer-based procedure.
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Planned Number of Observations
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Before
556 pupils aged between 8 and 10 years old.
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After
About 300 pupils aged between 8 and 10 years old.
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Power calculation: Minimum Detectable Effect Size for Main Outcomes
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Before
From the literature, we can assume that, prior to the intervention, approximately 50% of children in our context will consume at least one portion of fruit and vegetables in the school canteen (one out of two children). For the power analysis, we consider the following parameters: a Type I error rate α = 0.05, a power of 1 - β = 0.8, and a moderate effect size of 0.3. Consumption will be recorded twice a week for three weeks in each school, resulting in six observations per child during each phase. Data collection will follow a timeline based on four phases: baseline (before the intervention), during the intervention, post-intervention, and three months after the intervention — leading to a total of (maximum) 6 × 4 = 24 observations per child.
Expecting a 0.4 variation rate, with the above-mentioned parameters, 93 pupils are needed in each group.
Having multiple observations per child helps to mitigate potential absences during data collection. Hence, we plan for a sample size of 100 children per group, which allows for potential attrition over time, resulting in a total sample of 500 pupils.
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After
From the literature, we can assume that, prior to the intervention, approximately 50% of children in our context will consume at least one portion of fruit and vegetables in the school canteen (one out of two children). For the power analysis, we consider the following parameters: a Type I error rate α = 0.05, a power of 1 - β = 0.8, and a moderate effect size of 0.3. Consumption will be recorded twice a week for three weeks in each school, resulting in a maximum of four to six observations per child during each phase. Data collection will follow a timeline based on four phases: baseline (before the intervention), during the intervention, post-intervention, and three months after the intervention — leading to a total of (maximum) 6 × 4 = 24 observations per child.
Expecting a 0.4 variation rate, with the above-mentioned parameters, 93 pupils are needed in each group.
Having multiple observations per child helps to mitigate potential absences during data collection. Hence, we plan to have a sample size of 100 children per group, allowing for potential attrition over time, resulting in a total sample of 300 pupils.
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Intervention (Hidden)
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Before
The RCT tests the effect of food message provision on children's fruit and vegetables quantities consumed at their school's canteen.
We manipulate two dimensions in the delivery of the message:
1) The messenger: either a peer elected beforehand by the classmates, or the class' teacher;
2) The content of the message: it focuses either on health or on sustainability.
The messages are the following (translated from French):
Health-related:
" Want to feel good? Eat your fruit and vegetables!
Why? Because they come from nature, not from factories.
When you eat them all – even the ones you don’t like so much – your body gets stronger.
And that’s good for you, because they’re full of vitamins and have everything you need to have energy and stay healthy!"
Sustainability-related:
"Want to help the planet? Eat your fruit and vegetables!
Why? Because they come from nature, not from factories.
When you eat them all – even the ones you don’t like so much – you don’t throw them away.
That’s great for nature, because it saves the water and soil used to grow them, and you help protect the Earth!"
After the message is told by either a peer or the teacher, the menu of the day is also provided to the class. A poster with the main message (either "Want to feel great? Eat your fruit and vegetables!" or "Want to help the planet? Eat your fruit and vegetables" will be displayed in the classroom during the intervention days.
We will estimate and compare the effects of the different interventions on the quantities of fruit and vegetables consumed, as well as on overall consumption and food waste, measured by what was taken and what remained on the food tray. We will also conduct a heterogeneity analysis based on children’s characteristics, preferences, and social networks.
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After
The RCT tests the effect of food message provision on children's fruit and vegetable quantities consumed at their school's canteen.
We manipulate one dimension in the delivery of the message that is the messenger: either a peer elected beforehand by the classmates, or the class' teacher;
The message is the following (translated from French):
Health-related:
" Want to feel good? Eat your fruit and vegetables!
Why? Because they come from nature, not from factories.
When you eat them all – even the ones you don’t like so much – your body gets stronger.
And that’s good for you, because they’re full of vitamins and have everything you need to have energy and stay healthy!"
After the message is told by either a peer or the teacher, the menu of the day is also provided to the class. A poster with the main message ("Want to feel great? Eat your fruit and vegetables!") will be displayed in the classroom during the intervention days.
We will estimate and compare the effects of the different interventions on the quantities of fruit and vegetables consumed, as well as on overall consumption and food waste, measured by what was taken and what remained on the food tray. We will also conduct a heterogeneity analysis based on children’s characteristics, preferences, and social networks.
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