When Jack and Annie came back from their adventure in Magic Tree House #54, they had lots of questions. How do sled dogs race for so long? When was the first Iditarod? What are some other extreme sports? Find out the answers to these questions and more as Jack and Annie track the facts about the Iditarod, open water swimming, the Ironman triathlon, free climbing, the X Games, and other ways people test their limits.

Filled with up-to-date information, photographs, illustrations, and fun tidbits from Jack and Annie, the Magic Tree House Fact Trackers are the perfect way for kids to find out more about the topics they discover in their favorite Magic Tree House adventures. And teachers can use the Fact Trackers alongside their Magic Tree House fiction companions to meet Common Core text pairing needs.