Make sure wheel chair access is incorporated into trail design. A nature trail could eventually wind throughout the entire schoolyard. Regularly mowed grass trails are easily maintained in sunny areas. Design the trails to be at least as wide as the mower. A 6-foot width works well.
Wood chips are a good ground cover for wooded trails.
Many tree maintenance companies will provide free wood chips. It should be placed in front of bird feeders, wetlands, in meadows or along thickets for closer observation of secretive wildlife. Picnic tables can be used for lunchtime and as work stations. Place in an area that is easy to access from school. Hillsides are a good place for a small amphitheater.