I've seen the 4 groups before and it runs exactly the same as three groups, just less time per group. We have Novice, Intermediate & Advanced. Their grouping might be labeled as Beginner, Novice, Intermediate & Advanced. I have no real idea, but that's my take. Also, we have in the past, run two groups with 30 minute sessions. On those days, you really miss the 20 minute sessions.