I need some ideas on how to display (cheaply and efficiently) the http://www.eoearth.org/article/Natural_resource_quality to a class. One taken (and therefore not usable) example would be a sheet of math problems that have varying difficulties. If asked to do as many as possible in a minute, every person will choose the easiest problems first. Asked to do it again and again, the person will struggle with harder and harder problems, the number of problems completed each time diminishing. I'm going to keep brainstorming, any ideas are welcome.