From West Virginia to Arizona, public-school teachers are in revolt. They are demanding better pay, and they deserve it — so long as their salaries are tied to their performance.

It’s not that teachers in the United States are underpaid; the median income for the country’s one million high-school teachers, for example, is more than 50 per cent higher than that of the general population. But relative to peers with similar levels of education, teachers are falling behind.

In 1994, public-school teachers made only 2 per cent less than college graduates in other fields; by 2015, the gap was 17 per cent.

Cuts in state education budgets have made the problem worse. In more than half of the country, after adjusting for inflation, average teacher salaries have declined since the start of the century. In West Virginia, where pay has dropped by 8.9 per cent since 2000, teachers went on strike in late February, forcing lawmakers to pass a 5 per cent pay increase for the next school year. Teachers unions in Arizona, Oklahoma and Kentucky plan similar walkouts if their demands are not met.

To avoid such an outcome, which hurts students the most, both sides need to compromise. Teachers should not have to work second and third jobs to make ends meet, as many say they do, even in states with low costs of living. At the same time, pay raises should be accompanied with reforms that evaluate and reward teachers for the quality of their work.

In the vast majority of school districts, teachers’ salaries are determined by their educational backgrounds and years of classroom experience. Because they reward seniority, these pay schedules are fiercely defended by teachers unions. But they reduce the funds available for other priorities such as encouraging teachers to relocate to rural and low-income districts and addressing shortages of teachers in Stem subjects.

Across-the-board pay increases for teachers may go some way towards improving student performance, but not far enough. Despite opposition from unions, school districts in at least 30 states have introduced performance-based bonuses for teachers. In schools where teacher pay is tied to student performance, test scores have risen by the equivalent of three additional weeks of learning. Districts with merit pay are better able to hire strong, entry-level candidates and prevent high-performing teachers from leaving.

International comparisons bear out a basic, if self-evident, truth: how well students perform depends on how well they are taught. The US should pay its teachers more — and give the best ones incentives to show how much they are worth.