If you want to keep a species that specialized on a particular species of food plant make sure that this plant is always fresh and abundant available.

Particularly suitable to be kept at school are the caterpillars of the Silk Moth (bombyx mori). They can even develop in an empty shoe box, but a cage covered with gauze or fly screen is better. The caterpillars can be touched easily but eat a lot of leaves of mulberry trees.
If a school can't provide these leaves it cannot keep this famous silk producers that were historically so significant and even caused wars.

Then Oak Eggars (Lasiocampa quercus), close relatives of the Silk Moth, might be suitable. They also produce silk and can be fed with leaves of several species of oaks. Since there are oaks having green leaves all over the year on all continents, breeding is possible throughout the whole year. To keep the oaks fresh for a longer time they can be put in a glass of water in the cage. But be careful! The glass must be sealed up so that the caterpillars can't get into it. otherwise they would continue crawling in the water until they are drowned.

drowned caterpillars

Oak Eggar caterpillars also need oak leaves to pupate. They draw them together and spin their cocoons in the leaves.
We observed caterpillars in a glass box that tried to wrap the pane of glass around them until all their silk was distributed and used up. So they had to pupate on the floor without a protecting cocoon.

raster electron microscope photo of silk

With the breeding many observations can be done. Students compared silk produced by caterpillars and silk produced by spiders and got interesting results.