An average of $18 per student is paid out each year through the typical school soft drink contract. About 67 percent of the revenue collected from soft drink sales goes to beverage companies, not schools. (Schools earn commissions on sales and cash advances on the contracts.) Also, providers penalize schools for failing to meet sales quotas, giving administrators an incentive to encourage soda consumption. Result: Many of the largest school districts in the country have gotten rid of soda vending machines.
Links:
[1] http://www.edutopia.org/will-banning-sale-soft-drinks-schools-significantly-decrease-childhood-obesity-and-related-health-pr
[2] http://www.edutopia.org/making-nutrition-part-school
[3] http://www.edutopia.org/fighting-fitness
[4] http://www.edutopia.org/edible-schoolyard-school-garden-video