School report cards, a centrepiece of the Government's education policy, have run into major problems in New York, the city where they were developed.
Last week, 97 per cent of New York's elementary and middle schools gained either an A or a B grade on their report cards.
The results render the grades virtually useless for their main purpose of helping parents to rate and choose between different schools.
Red-faced education officials in the US city now admit they may have to change the system to ensure that schools receive lower grades next year.
The news is also an embarrassment for the Department for Children, Schools and Families officials who, as The TES first revealed a year ago, were inspired to introduce report cards to England after a visit to New York.
They are designed to give parents a more balanced view of schools by including a range of indicators such as pupil opinions, attendance and comparisons with similar schools, alongside test results.
DCSF ministers have touted the cards as a fairer alternative to league tables, although they have baulked at getting rid of tables altogether.
The idea of summing up all the information on a report card in a single grade has always been controversial. Earlier this year 57 per cent of respondents to a DCSF report card consultation said they were opposed to them including overall ratings or grades.
Ed Balls, Schools Secretary, said he wanted grades so the cards could be used by the media to rank schools.
"I don't think a fair and easy ranking can be done without a single grade," he told journalists.
But the New York experience shows how difficult that can be with a single grade.
Beyond the obvious problem of grades A-D or F being a blunt comparison compared with the percentages used in league tables, it has highlighted the tricky issue of what happens when the vast majority of schools get the same grade.
The problem has developed in New York in just three years. In 2007, the year the cards were introduced, 23 per cent of elementary and middle schools in the city scored an A. In 2008 that climbed to 38 per cent and this year it shot up to 84 per cent.
Shael Polakow-Suransky, from the city's education department, told The New York Times the system would be adjusted because he wanted to see a wider distribution of grades. "We are going to raise the bar," he said.
The DCSF plans to introduce report cards in England from 2011 after a two-year pilot.
Mick Brookes, National Association of Head Teachers general secretary, said: "This confirms what we have always said about a single report card grade.
"It is misleading and would not be any use to parents. It proves the old adage that to every complex question there is an answer that is simple and wrong."
A DCSF spokesperson said: "We believe a single overall grade is important to show a clear definitive view of a school's effectiveness among all stakeholders.
"Without an overall grade there is little hope of removing the relentless focus on a single academic indicator, which provides only a partial account of what schools do.
"But any final decision on whether or not an overall score or grade should be used in the school report card will not be made until after the pilot is ended."
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