To raise a caterpillar through the chrysalis or pupa to the adult moth or butterfly is an excellent lesson about insect metamorphosis. All you need is a caterpillar, some of its favored food, and a suitable container. You can find caterpillars on most plants during the spring and early summer. Put the caterpillar and a few fresh leaves in a wide mouth jar or plastic shoebox. Cover the jar mouth with netting or a piece of nylon. Every day change the leaves and provide dry paper towels to help prevent mold. You can put in pencil-size twigs upon which the caterpillar can attach its chrysalis or silken cocoon (with the pupa inside). The insect will hatch in 10-14 days, if it does not over winter. Before releasing it you can photograph your prize. Don't be disappointed if small wasps or flies--natural parasites--hatch out instead. These insects keep the butterfly and moth populations under natural control.
For more extensive and species-specific information, go to the excellent Raising Butterflies site.