I would suggest larger groups, in case you have any that pass away.
My students have choosen to do agriscience fair projects on this, I have never done it as a class. The varieties that they have come up with were: reg feed vs. medicalted feed, feed with a veggie supplement, and then chick grower/finisher vs. an egg layer feed.
I would suggest that you go through a bag of starter with all the chicks and then start your feed trial after that. That is how I have had my ag science fair kiddos do that before. We just purchase a 50lb bag of start and once it is gone, start your feed trial.