How did private industry get involved in the school lunch program?

In 1970, the American School Food Service Association (ASFSA) persuaded the U.S. Department of Agriculture (USDA) to launch a pilot program in which private food-service providers would take over and administer lunch programs at participating schools. Contracting with food service providers could also solve a problem that had plagued the National School Lunch Program since its earliest days: how to feed hungry children whose schools did not have the space or equipment to operate cafeterias. Instead of building their own industrial-scale kitchens, these schools could save money by contracting with food service companies to prepare, freeze, and deliver meals that could be easily reheated and served to students at a much lower cost. Within a few years, the USDA fully embraced this approach, changing NSLP rules to allow all participating schools to turn their cafeterias over to private food-service companies. In the same years, the National Soft Drink Association pushed through another significant “reform” to the NSLP: an amendment that eliminated restrictions on so-called “competitive foods” that had barred the sale of name-brand food products at schools. Schools could now negotiate with soda and snack distributors to install vending machines on their campus and, in some cases, to secure “pouring rights” for soft drinks in school cafeterias, often in exchange for significant donations to those school districts. Within just a few years, almost half of American high schools had vending machines with soda and candy on site and by 2000, snack foods were available in vending machines at 43% of elementary schools, 75% of middle schools, and 98% of high schools across the U.S.

Janet Poppendieck, Free for All: Fixing School Food in America (Berkeley: UC Press, 2010): 62.
Susan Levine, School Lunch Politics: The Surprising History of America’s Favorite Welfare Program (Princeton: Princeton University Press, 2008): 160-163, 182.

How did private industry get involved in the school lunch program?