If you do a lesson using recycled materials...you can also introduce the artist who created the works making up the installation at the Smithsonian "the Thron of the Thir Heaven of the Nations Millennium General Assembly" by James Hampton. His story is so wonderfully inspiring. Also you could focus on the Watts Towers and there is a wonderful artist (sorry I don't remember the name) who lived on Mahattan's East side and would get tires from blow outs on the FDR and she created these wonderful sculputres!
One lesson for students...is that art can be anything! Or the question is...what makes it art?