Here is something that I think might be pretty easy, but I am pulling my hair out over it. I have 200 students who I divide up into 25 groups of 8 students each. After 10 weeks, I scramble the students into 25 new groups, but each group must be composed of students who did not have each other in the previous groups. After 10 more weeks, I scramble the students again into 25 new groups of 8, but each group must be composed of students who did not have each other in any of their two previous groups. I do this for two more trials. Any idea how to do this? Color me GROUP PERPLEXED!