If you are interested in observing the Swallowtail butterfly you will need Parsley or Dill beds and you will need to plant them every other year as they are bi-annual. Once the cycle is up and running we have parsley returning and the Swallowtails with it. We haven't had much luck with bringing the Swallowtail into the classroom and waiting for spring emergance. In fact we're batting zero in my room and have only 1 hatched in another classroom. They seem to do better if left outside in their natural environment.
If you are trying to attract a specific butterfly, find out what type of plant it lays its eggs on and what it eats and plant those in your garden. It's a lot of fun and the children really get excited and involved. We even have Hummingbirds visiting and we have added plants to attract them as well.
Just remember, it's not as difficult to start a butterfly garden as it might seem. It's a lot of physical labor but the feeling of satisfaction and enjoyment of the finished product far outweigh the sore muscles. When the soreness leaves you still have the finished product to enjoy for years to come!