Mr keating tells Cameron Pitts and Knox to walk in a circle to show them that

Mr. Keating wanted the boys to realize how difficult it is to be an individual when you're pacing yourself with someone else. Walking in a circle was a lesson in complacency..... simply following along. It didn't allow for differentiation. T elling the boys to break the circle and walked as they pleased was a lesson in individuality, maintaining one's own beliefs, and walking one's own way. It illustrated Keaton's belief that no matter what anyone says, people need to live their own lives.