A while back, I wrote:
. . . many school children have to eat lunch as early as 10am! In many schools (including my own kids’ school), children have to be run through the cafeteria so quickly they hardly have time to eat. Couple that with the new federal guidelines limiting the number of calories that can be served, and it is no wonder many kids are starving by the time school gets out and beg to go to McDonalds!
In addition all the above, I'd also add that because of increased curricula requirements, PE has been cut to the bone in most schools.
Alas, it seems most of the discussions I hear about improving childhood health in schools revolve around "sexier" headline-grabbing issues like serving more fruits and veggies, serving more local foods, zoning rules, banning sodas, teaching gardening, and so on. It may just be that the less "sexy" (and potentially less costly) issues like encouraging exercise, increasing cafeteria time or size, or giving a small afternoon snack, may be more promising.
Of course, we'd want empirical evidence that length of lunch had a substantive impact on dietary choice and weight. I see one piece of evidence was just published in the Southern Economic Journal this month. The piece is by Rachana Bhatt entitled "Timing is Everything: The Impact of School Lunch Length on Children's Body Weight." The abstract
The large number of overweight children in the United States has prompted school administrators and policy makers to identify practices in schools that contribute to unhealthy weight outcomes for children and develop strategies to prevent further increases. Advocates for school nutrition reform have suggested that it is important for children to have an adequate amount of time to eat meals in school in order to maintain a healthy weight. This article examines whether the length of time children are given to eat lunch in school has an impact on their weight. I find evidence that an increase in lunch length reduces the probability a child is overweight, and this finding is robust across various econometric specifications, including a two-sample instrumental variable model and difference-in-differences model that account for the potential endogeneity of lunch length.
The paper indicates:
extending lunch length by 10 minutes is associated with a 1.2% reduction in BMI, and it reduces the probability a child is considered overweight for his/her age and gender by 2.4 percentage points.
I'll be curious to see if these results hold up in randomized controlled trials.