Over the past 100 years, visitor learning at America's national parks has grown and evolved. Today, there are over 400 National Park Service (NPS) sites, representing over eighty million acres. Sites exist in every US state and territory and are located on land, at sea, in remote areas, and in major urban centers. Every year, more than 300 million people visit national parks, and several million of them are children engaged in one of many educational...