America’s two largest states - California and Texas - have thrown their weight behind proposals to link teachers’ wages to student test scores, lending further impetus to growing US support for controversial performance-based pay.

The schemes, being pushed by the governors of both states, come on top of calls from President Bush for $500 million (pound;261m) for schools to introduce merit pay into seniority-based salary scales.

“Excellence should not be rewarded the same as mediocrity,” Texas governor Rick Perry declared last week, trumpeting a $150m-a-year initiative that would offer $7,500 bonuses to the state’s 300,000 teachers if students meet testing goals.

The remarks came just weeks after California governor Arnold Schwarzenegger called for staff pay to be “tied to performance, not just turning up”.

Merit pay was championed by both President Bush and Democrat challenger John Kerry during the US election campaign and was the chief recommendation of a blue-ribbon education reform panel composed of leading executives and lawmakers, earlier last year.

San Francisco schools chief Arlene Ackerman said last month incentives were needed to “reward those who work the hardest, perform the best, or whose skills are in greatest need”.

Critics of merit pay say that it has had a mixed track record in the places where it has been implemented.

A scheme tying pay to performance appraisals in Cincinnati was scrapped after just two years in 2002 amid protests that it was divisive and prone to favouritism.

A 1999 California scheme lasted no longer, incurring similar staff hostility without clear-cut effects on academic results. Two thirds of US teachers backed bonuses for hard work in a 2003 poll, but most opposed tying them to test scores.

The California proposal retains some staff evaluation but is heavily based on student performance on standardised tests. In the US pupils face standardised tests every year from age seven to 13 and there are plans to extend annual tests up to age 17.

In Texas the bonuses will be dependent solely on test results.

Bruce Fuller, professor of education policy at the University of California, Berkeley, warned that these approaches are unproven and could “pit teacher against teacher” as there would be competition to get the best students.

And the scheme could make it even harder to recruit teachers in inner-city schools with lower test scores, he added.

Measuring progress would entail administering tests at the start as well as end of the school year, when testing is already considered by many to be too intensive, said Prof Fuller.

Getting unions to agree would be key, he predicted.

America’s most closely-watched merit pay scheme, introduced with union support last year in Denver, lets staff choose their own performance yardsticks.

But union endorsement was not forthcoming last week in Texas where the state teachers’ association chief, Donna New Haschke, said the proposals would “reward those who teach to the test”.

Concerns have also been raised that upping the stakes on tests that already have jobs and funding riding on them, under Texas’s accountability system, could further encourage staff to cheat. An investigation is under way into widespread test cheating by teachers there.