Race the Wild #2: Great Reef Games
The science in this is every bit as good as it is in the first book, and there are lots of interesting facts about the Great Barrier Reef. There is also a very good lesson on symbiosis, or mutualism, that students will understand because of all of the examples that are mentioned, and the brilliant part is that it is woven into the story in a way that it doesn't seem science-y at all!
Sage's difficulties add to the interest of the book but are not dwelt on too much, striking a good balance for early readers. Readers who are intrigued by Gordon Korman's Dive or Island series or Spradlin's Killer Species books, or who have a fondness for Jean Craighead George's work will find this adventure to be a satisfying dip in exotic waters!