As a teacher with a Masters Degree and over thiry years experience who has worked as a construction labor in the past can relate a person who walks off the streets to do labor does not know the building codes so they can't run the construction company or be a foreman, a person who just walks off the street can not run a classroom which has its own set of laws and professional codes. Yes as far as personalities go, many teachers may well have done better in the trades and many people in the trades may be better suited as teachers, but each person still has to learn the rule and codes of his profession to be put in charge and not just a helping hand.