I love the responses I'm reading! about eight years ago, we (as a State in Oregon) didn't have any protocols or procedures for food safety pertaining to the school garden, so I went about creating our own. When in doubt, you should always defer to your local Health Department and follow any State regs. you may have.. We had our State Health Department "sign off" on our plan, so it was peace of mind.
So having said that, as far as eating or grazing right out of the garden, I use this analogy. If I make myself a sandwich, I don't need to worry about documenting anything or being strict about the Health department rules. If I make YOU a sandwich, then I really need to pay attention to document and follow my procedures! So that gives the go-ahead for our students to "graze" as long as the instructor knows what s/he is doing and the kids only eat what the instructor directs them to, or they ask permission first. When HARVESTING for the cafeteria, farmer's market, etc. strict standards need to be followed such as washing hands, excluding kids from the garden who are sick (they shouldn't be at school anyway), using washable harvest containers, etc.
I agree that the instructor or at least the school garden coordinator nearby should be certified in a food safety course / have food handler's card.