From personal experience yelling at kids does not get them to perform any better. The reason staff members yell is because they've run out of ways to get the material across so they instinctively yell to try to get the idea into the kid's head. If I ever had a staff member verbally abuse one of my students I would have him fired. There is no reason to yell at kids just because the teacher is getting frustrated, no matter how competitive this activity is, yelling doesn't get anyone anywhere. If anything, more mistakes occur as a result of yelling...just my "new school thought process" .02 cents.