Abolishing school league tables leads to worse academic results, especially for pupils from poorer backgrounds, research released this week suggests.
Test results in Wales have fallen by an average of two GCSE grades per pupil compared with England following the scrapping of secondary league tables in 2001, researchers from Bristol University found.
Students from deprived backgrounds fared the worst, with the strongest impact among schools with the highest numbers of pupils eligible for free school meals. In the worst-performing 25 per cent of schools, pupils suffered a fall of three GCSE grades compared with English peers.
The news comes as the Government publishes the terms of reference for an inquiry into the future of national tests at key stage 2 (see box).
The Bristol report, produced by the university's Centre for Market and Public Organisation, said: "We find systematic, significant and robust evidence that abolishing school league tables markedly reduced school effectiveness in Wales."
Report co-author Professor Simon Burgess added: "School accountability policies such as league tables seem to be a cost-effective way of raising school performance, particularly for students in disadvantaged schools and neighbourhoods." He said results suggested league tables put pressure on low-performing schools to "raise their game".
Teaching unions in England rejected the findings, describing the report's methodology as "flawed".
Chris Keates, general secretary of the NASUWT, said: "It is wrong implicitly to criticise the commitment and hard work of teachers and schools in Wales on the basis of such a questionable piece of research."
Ms Keates criticised the research for not factoring in other variables, such as the funding of local authorities or other intervention strategies.
Russell Hobby, general secretary of heads' union the NAHT, said: "All measurement systems distort behaviour, often with significant, unintended and undesirable effects.
Mr Hobby said the findings did not undermine the campaign to abolish KS2 national tests.
But in Wales it appears likely that tougher forms of school accountability will be introduced to help improve performance.
Officials have acknowledged that the scrapping of league tables cost Wales the ability to effectively hold schools to account and share best practice. More pressure is likely to follow next month with the publication of the international Pisa (Programme for International Student Assessment) rankings, in which Wales is widely expected to perform poorly.
Education minister Leighton Andrews said: "In Wales over the decade of devolution we have implemented most of the changes the profession wanted. So we don't have league tables. We will see in December when the international comparisons of school performance are reported in the OECD's Pisa survey whether that approach has paid off."
DETAILS OF INQUIRY ARE REVEALED
The panel responsible for the long-awaited review of key stage 2 Sats will include phonics guru Ruth Miskin, founder of the popular Read Write Inc. programme.
She will be joined by Miriam Rosen, former executive director of Ofsted, on the panel, which will be chaired by Irish politics professor and cross-bench peer Lord Bew.
The inquiry, which will look at how to reduce teaching to the test - a major criticism of the current system - will take evidence over 12 weeks. The panel also includes primary heads and one secondary school head. Their report is due to be submitted to Education Secretary Michael Gove by June 2011, after the next round of KS2 tests in May. The NUT and heads' union the NAHT led a boycott of the tests this year, supported by one in four schools.