* The country: School meal programs differ greatly across the globe. Portion sizes and types of food served vary widely.
* The specific meal: A heavier meal like a roast dinner will weigh considerably more than a lighter salad.
* The school district/school: Even within a single country, individual schools or districts may have different standards or approaches to portion sizes.
* The specific menu item: A chicken breast will weigh more than a serving of vegetables.
To find an approximate weight for a *specific* school's meals, you would need to contact that school's food service department. There isn't a readily available global average.