I don't know how long ago you are talking about, but I am pretty sure nowadays most schools go through contractors too for cooks and janitors (I actually did not go to school in the US so correct me if I am wrong)
Cooks:
https://www.linkedin.com/jobs/view/food-service-worker-i-at-...
Custodians:
https://www.glassdoor.com/job-listing/substitute-custodian-m...