Fall/Warm colors collage

I haven't actually tried this one myself, but I think it would be fun this time of year. 

This idea came from my favorite art idea website: Art Projects for Kids. 

The author has full instructions listed there.  (You would need to supply the tissue and wax paper for the class).  I would like to try tracing and cutting out a leaf design on the collage and then hang it from a window to let the light sine through the colors.  You could have a discussion with the class about warm colors and collage techniques.