We recently got together with my sister, who also homeschools her children and decided to build some out of play dough. This time we learned about Atoll (A ringlike coral island and reef that nearly or entirely encloses a lagoon) and Archipelago (A large group of islands).
We had fun creating them~ the kids really enjoyed making them. When you do a hands-on project, it tends to stay with them longer. We'll be doing more of these fun projects...stay tuned for the next letter!