As you are studying trees and leaves this fall season, consider supplementing your curriculum with the free materials from Life of the Forest. They are offering one free set of posters plus handouts to a teacher at a time. They are in full color and can supplement your natural observations of the outdoors.
For example, ask the children to look for leaves outside or to bring in some from home. Use the leaf poster to identify them. Do the same with the seeds poster. Older students can benefit from some of the other lessons from International Paper.
I saw the posters from about 7 or 8 years ago and they were fairly decent. Order a set and see what you can do with them. Let me know what you think!