If you want to raise butterflies in your classroom, you can either order larvae through a science supply or nature catalog, or you can collect eggs or larvae outside and try to raise them indoors. In either case, time it so that the mature butterflies can be released as nectar flowers begin to bloom outdoors in the spring.
Although butterfly eggs may be hard to find outdoors, you may observe a female laying eggs or find a caterpillar on its host plant. In either case, make sure to bring in some twigs of the host plant so the caterpillar can continue to feed. Indoors, you and your students will want to recreate the environmental conditions that the young butterfly would find in the wild.
Containers must have food, air, humidity, and a comfortable room temperature out of direct sunlight. An aquarium with a screened lid, a large glass jar with holes in its lid, or a cardboard box with screening will do. Use a large enough container so a mature butterfly can expand its wings.
Keep the container relatively humid, but not too wet. Place a moist paper towel or newspapers in the bottom to maintain humidity. Keep the caterpillar supplied with leaves of the plant you found it on, or research other plants that species will eat. Clean out caterpillar droppings regularly from the bottom of the container. Extra twigs in the container will offer the caterpillar a place to crawl as it begins to pupate. Once the butterfly emerges and its wings are pumped up with fluid, move it outside, open the lid near your sanctuary, and hope that he or she likes the buffet.