Oh how fun!!! We got The Prairie Primer and I would LOVE to do that this year (we might do it next year because I already have plans for this summer school, so this will be NEXT summer school).
Anyways, I found this really fun looking Guide To Pioneer Projects You Can Build Yourself. It is on sale for $12, normally $15 right now. :D AND the sample pages they show you are NICE! Some show you like one or two things. This gives you a GREAT feel for what you will be getting.
So if you don't have a theme yet for the summer, you might look into getting yourself some Prairie Primer and/or the Guide To Pioneer Projects You Can Build Yourself and have a BLAST this summer!