Some people might not object to a high school science teacher getting paid more for having a master's degree in biology.

Or raising the salary of an educator who has learned another language.

But should teachers be able to boost their salaries for going to the opera to enhance their music appreciation? Or for attending union conferences?

Los Angeles Unified spends $519 million each year - or a quarter of the teacher payroll - on salary bonuses for teachers who have taken additional coursework, according to a report released last week. Those classes range from graduate courses taken at a university to online seminars and art appreciation classes.

The salary enhancements are coming under increased scrutiny by the school board as it faces yet another year of shrinking budgets.

"There is a role for ongoing learning ... but unless there is a direct correlation to student achievement, I don't know if it's worth the investment," said LAUSD school board member Yolie Flores.

The "salary credit" system is not unique to Los Angeles Unified. In fact, most school systems in the country