Good for you and your school for adding native habitat to your school's landscape. The simple answer to working with red clay is to add organic matter to the soil, and lots of it. For the long answer read Improving Clay Soil by Keith Baldwin. Contact an organic farmer or an organic home gardener in your area and seek his/her advice; perhaps they would visit your school and explain the process in person.
You have several options for the supporting structure around your beds (consider making them more kidney-shaped instead of geometric shapes for a more natural look). You can choose rocks, Arsenic-free pressure treated landscape timbers, or recycled plastic timbers. All will not leach harmful substances into the soil and are safe for children and adults to handle. For instructions on building raised beds, search the Web using the heading "raised bed construction."
As for butterfly gardening itself, see our Backyard Wildlife Habitat section for lots of information on natural gardening. Use our LocalGuides to help you find wildflowers for your area. Visit a local native plant nursery for advice on plants to select.
Once you have done all of that, and have become more familiar with resources available to you both in Charlotte and on the Internet, then visit the National Wildlife Federation Schoolyard Habitats website for a vast amount of information and support created especially for you! There are quite a few NWF certified Schoolyard Habitats in North Carolina, and here is information and a photo from the habitat in Marion, North Carolina. Consider ordering the Schoolyard Habitat Starter Kit and then off you go. Good luck!