For some strange reason, my undergraduate training didn't include one of the most beneficial theories in the field. While Piaget and Erikson are quite necessary, once the brain has stored them and they are easily recalled in a manner which positively influences a person's teaching, then they have done their job. Unfortunately, not much teaching can occur without the most important component of real life in the classroom: management.
Thank God for Harry Wong! This man is not a professor or even a doctor; but his knowledge and expertise have saved the careers of many would-be-ex-teachers, yanking them out of the statistical gutter with his wit and practicality.