Live and learn. Experience seems to trump everything when it comes to American salaries in education. The older teachers are, the more they make — compared to employees in most fields, who see pay gently decline after peaking in their 40s. Union rules and government regulation mean young teachers make the least in their already low-paid profession, which may explain why 13.5 percent of them drop out. Could changing the rules to spread the wealth boost retention rates, or would that simply make more mature teachers cut class?