As a director in a gym, I feel the best classes to train new coaches on is our 3 year old classes. New coaches always feel that is impossible in the first couple of weeks, but after a month and a few helpful hints from some veteran coaches they become their favorite classes. The coaches who can't hack a 3 year old class usually suffer the highest student turnover rate. Teaching 3 year olds really teaches you how to work with all ages, and reminds you how important variety is to every class and practice. I feel the best coaches are not those that can teach the highest level of skills, but the one's who can work with largest variety of levels.