With a massive teacher shortage looming, the idea of paying more for top teachers is beginning to make a comeback in several states.

Some school districts (education authorities) are experimenting with paying teachers bonuses tied to their performance. But there is dogged and well-organised opposition from the teachers.

Even though the best would benefit, teacher unions have opposed the idea of merit pay, which they argue is a way for school systems to avoid paying decent salaries across the board.

“The truth is, we don’t believe it does provide an incentive,” says Kathleen Lyons, spokeswoman for the National Education Association, the largest US teachers’ union. “If the issue is, how do you get good people into the classroom, you need a consistent approach, not these little silver bullets.”

The most ambitious attempt to link pay with performance also was its biggest failure. The Washington DC suburb of Fairfax County, Virginia, adopted a programme in 1986 that boosted pay to top-performing teachers, based on peer evaluation, but abandoned it because of cost and teacher opposition.

However, teacher shortages have spurred new attempts to attract staff through performance pay and bonuses. Two million new teachers will be needed within the next 10 years, according to government estimates. This is partly because 22 per cent of teachers quit the profession within five years of entering the classroom - 50 per cent in urban areas.

Massachusetts is offering bonuses of as much as $20,000 (pound;12,500) for highly qualified teacher candidates.

But the latest battleground for merit pay is Los Angeles, where the school district is demanding that teacher pay be tied to improved pupil performance.

The teachers’ union has countered with a watered-down proposal under which all teachers would receive an extra 1 per cent in pay if there was city-wide improvement in, for example, the drop-out rate.

“I have yet to see a system that is really fair, and unless it’s fair, teachers won’t accept it,” says Day Higuchi, the LA teachers’ union head.

Teachers in Hernando, Florida, turned down a plan that would have given them cash bonuses if they scored well in their reviews, saying the administrators who evaluated them were too subjective.

In other areas performance pay has been imposed over the objections of teachers, especially since a 1996 report of the National Commission on Teaching and America’s Future recommended providing salary incentives for demonstrated skills and knowledge.

The Georgia board of education has approved $2,000 merit bonuses to teachers who help students meet academic goals. In Robbinsdale, Minnesota, it was taxpayers who decided to end the practice of giving new teachers automatic pay raises, demanding instead that they submit portfolios proving their competence in exchange for salary increases.

In Kentucky, schools that exceed their improvement goals receive bonuses to spend as they see fit. Last year, more than $27 million was paid out, and almost all of the money went toward bonuses for teachers.

And in New York, a business group has offered $30m in incentives to teachers and administrators whose students achieve good test scores.