PUPILS in England are getting used to unscheduled breaks. On March 26th the National Union of Teachers (NUT) struck in protest at an overhaul of pay structures that is due to begin in September. This will end automatic pay rises for senior staff, giving headteachers more sway over pay levels. Up to a third of the country’s schools were closed or partially shut.

More is at stake than fairly small amounts of variable salary. After rows over changes to pensions, pay variation is the latest turf on which Michael Gove, the bullish education secretary, has fought with the unions over how to run schools. The NUT says the new deal breaks a long-standing pay “spine” dating back to the 1920s and will undermine esprit de corps.

In theory, academy schools, which now account for half of all state-funded secondary schools in England, have a good deal of autonomy over staff wages and working conditions. In practice, most have stuck to existing national agreements. But that is changing. Liam Nolan, head of the Perry Beeches chain of academy schools in the West Midlands, has embraced performance-related pay across all staff levels, “because it sends a strong signal that you are not accepting excuses for failure”. High-flyers at his chain of schools are encouraged to gain master’s degrees. Financial rewards and promotion await those willing to put in the effort.

Evidence for the usefulness of performance-related pay varies. A cross-country comparison by Ludger Woessmann at Munich University concluded that education systems with some element of payment by results had an advantage in core subjects. Some of the best performers in international league tables, such as Finland and Shanghai, link rewards to outcomes. Even in some that do not, like Singapore and South Korea, the best teachers top up their salaries by tutoring exam candidates after school hours.

Many well-aired objections to variable pay have been muted by changes to English education. Better-moderated exams, with fewer modules marked by those who taught them, have scotched fears that teachers might be inclined to mark generously to boost their results. Improved data about how pupils progress from primary to secondary school has made it harder to argue that factors like parental input and natural ability determine results more than sound teaching does. A study by the Varkey GEMS research foundation found that Britons were much better disposed to payment by results than the average in other OECD countries.

The objection that merit pay will undermine collegiality is a little more plausible. But widening the criteria by which teachers are judged can deal with this: team players as well as ambitious individualists might be rewarded. Beyond the permanently outraged teachers’ unions, many staff admit that the old “escalator” approach made it hard for those promoted to upper pay scales to step down again if they struggled with leadership.

The new power to vary teachers’ pay underlines a shift in the role of headteachers from administrators to leaders, who can exercise their own judgment about staff and much else besides. That is what irks opponents. But it might be a useful part of the recipe for better schools.