If you are interested in creating an outdoor classroom, the following are great resources to help get you started.
National Wildlife Federation
The perfect starting place. The National Wildlife Federation provides excellent resources to help you learn about schoolyard habitats, spark ideas to create a certified schoolyard habitat, as well as provide lesson plan ideas for you to use with your students.
Evergreen
This Canadian organization has an abundance of school ground greening resources for teachers, including planning and design information, lesson plans, maintenance tips, case studies and much more. Don't start from scratch - let Evergreen help!
Boston Schoolyard Initiative
Great Outdoors Colorado (GOCO) recommends the planning resources from the Boston Schoolyard Initiative to help with understanding GOCO's School Play Yard Initiative. Check out before and after photos for inspiration, and review BSI's outdoor classroom planning and design workbooks.
The Acorn Naturalists
The Planning Guide for Habitat Enhancement on School Grounds will help you involve your students with the planning, implementation, and maintenance of your project through expanding upon activities developed by Project WILD.