I stumbled upon this one by accident, and I am thrilled! Weekly Reader has a new program this year called uBoost. Schools can sign up for a free subscription this year. You sign up your students and they can take a quiz for each issue of the Weekly Reader magazine you choose. They earn points by doing this which you can use for items for your classroom or incentives for students. Right after signing up I saw I had been given 2500 points which I could (and did) redeem for a $10. Amazon gift certificate. Save up your points and get 3 of them as any purchase over $25. at Amazon gives you free shipping.
Homeschools- The offer doesn't specifically exclude your school, so go for it!
Weekly Reader uBoost
Update 11/22/07- It appears uBoost has run out of Amazon gift cards for now.