Photojojo presents a great page on playing games with photography. These games are intended to express and develop photographic creativity.
While these games would work well in a photography or graphic design course, they are easily transferable to your average art course. Using drawing from a book, magazine, or a portfolio, or even ones you draw on the spot you could award points for the most appropriate or most interesting responses. The competitive nature of these games is likely to keep most kids interested in them. They could be used as warmup activities to start the creative juices flowing, or full blown assignments if you chose.
Art doesn’t have to be a solo activity but can easily be competitive and done with or against other people. Since kids, especially high school kids, are social by nature, this should make art that much more interesting.