Chemicals are toxic and abound everywhere. People apply pesticides and herbicides often without thinking about the consequences. The purpose of your organic edible schoolyard garden is to connect students with both nature and their food supply. It is also a place for thoughtful contemplation for the students. Commit to using natural means to control pests.
Most insects in your garden are beneficial, so you want to isolate the unwanted pest rather than blanket spraying everything. Not every pest needs to be sprayed. Caterpillars can be hand-picked off tomato and other plants.
Mild soaps and vegetable oils are a good option. Soap needs to contact an insect to kill it. It is a physical damage to the insect not a poison. That is why you need to apply the soap directly to the insect. Oils work the same way and accomplish the same goal. Oils are a good means to get rid of scale on a plant.
There are many natural insecticidal soaps and oils available commercially. You can also make your own by mixing 2 tablespoons of a mild soap in a gallon of water. You can create an oil spray by mixing the same ratio of vegetable oil in water. Some people add ground garlic or cayenne pepper to their sprays. I have some how-to videos on my YouTube – My Earthprints Channel under the Garden playlist, if you are curious to see how they do it.
Reduce your chances of a pest outbreak by following the principles of companion planting and creating a garden full of biodiversity. If you have only tomatoes in your garden (monocropping), then your plants are more susceptible to a tomato pest.