I just reviewed a terrific book about gardening and kids for my self-sufficiency blog.
Potatoes on Rooftops by Hadley Dyer could be used as a classroom project and covers where food comes from, starting a community or rooftop garden, composting, rain barrels, solar power and so much more.
The author has a fast paced, entertaining style that would appeal to kids, I think.
I believe that kids need to learn the skill of gardening. It can become a hobby or passion and might just save them lots of money in the future, besides the idea of knowing where their food comes from.