Classroom Classifieds, a new web-based business, gives school districts classified advertising web pages on which community members can sell unwanted goods in exchange for donating part of their proceeds to the school system. Classroom Classifieds works on the honor system. Those posting ads agree to donate anything from 1 percent (or less) to 100 percent of the sale to the education foundation. Participating schools are charged fees for creating the web pages and the amount of ads that run, but the company says schools can offset the costs with their donations. A basic site, with 100 classified ads a month, costs $20 per month.