At first I didnt quite understand but now I do. You want a rank within the class not ranking the actual class. Hmmn apart from applying a sort and then having a formula reference just those cells I am unsure how to accomplish this with formulas. a VBA script could certainly do it but I am trying to not suggest those as much as some people only want simple solutions. Anybody else have an idea of using a combination of sumif to rank each value within the class?
Otherwise I think VBA is your answer.