This is the exception, not the rule. Teaching is much more structured and regimented than you might imagine. Curriculum is often dictated by a school board or state board of education. People don't become teachers to get rich, but your salary can vary dramatically depending on where you work. Traditionally private school teachers are paid much less than public, although at some schools these jobs come with a place to live and meals included in your hiring package.
Salaries rise according to experience and additional education.
However, an advanced degree does not mean a giant increase in salary.