Because of the low starting salary, teaching is considered a poorly paid profession compared to other careers involving similar background and education requirements, such as registered nurses or accountants. Arne Duncan, the U.S. education secretary, has said that public-school teachers are “desperately underpaid,” and has advocated for doubling their starting pay.

“Most teachers do need the extra money and they do work in the summer,” says Richard Ingersoll, a professor at the University of Pennsylvania’s graduate education school whose research focuses on the teaching force; he cites data suggesting the majority of them even get actual summer jobs. According to Ingersoll, the average teacher’s earnings (including any money earned through summer work) are still lower than that of other professionals even when accounting for time off. And several studies have shown that low salaries are a top reason teachers leave the profession.

Still, research on the adequacy of teacher pay is adequate has gotten mixed results. Jason Richwine, of the Heritage Foundation, and Andrew Biggs, of the American Enterprise Institute, have argued that teachers are overpaid—or, at least, aren’t justified in complaining about their salaries—citing that a teacher’s salary amounts to about $1.50 for every $1 that they could earn in a private-sector job and that their skill sets are more limited than that of the average worker.

Another one of the main reasons cited by Richwine and Biggs, among other critics, is that teachers enjoy a big break each summer.

It’s true that, relative to employees private-sector careers, teachers in America tend to work fewer days. According to a U.S. News and World Report op-ed arguing against higher teacher salaries, the average private-sector employee works 260 days a year, while the average appears to be slightly less than that for public-sector employees. But educators like Klem tend to agree that having an extended break from classroom instruction (as opposed to paid time off here and there) makes the challenges of the job more manageable. And that break from instruction doesn’t always mean a summer vacation of idle R and R.

For the most part, the charter school at which Klem currently works follows Tennesse’s traditional public-school calendar, only adding a few extra days at the beginning of the fall to include the time teachers spend in professional development before students arrive. But again, that calendar doesn’t factor in the summer hours. Klem says she’s spending the rest of her summer this year attending meetings, developing school curriculum, helping train new teachers, and contacting families of her students, among other tasks. Past summers, she says, have been equally busy: graduate-school coursework to complete her master’s degree (which isn’t required but can mean higher pay), classroom organization or relocation, and so on. While some of these responsibilities come with a stipend, teachers say they’re relatively negligible given how much time they take—no more than $1,000.