By Katherine Sellgren
BBC News, at the ASCL conference
Mock-up of what a card might be like
Head teachers have unanimously rejected the idea of schools in England being given an overall grade under a new system of report cards.
The Association of School and College Leaders said it supported the concept of the cards but rating a school would be potentially damaging.
Report cards are used in the United States to measure pupils' achievement and well-being.
Ministers are consulting on how report cards would operate in England.
Education Secretary Ed Balls has visited New York, where schools' annual reports are given a single overall grade from A to E, with a F for fail.
But this use of a single grade is still controversial and, elsewhere in the States, it is not used.
The report cards are likely to be a Labour election pledge.
Association of School and College Leaders (ASCL) general secretary Dr John Dunford said annual report cards could work as a fairer alternative to the current scheme of publishing school league tables.
"It is a vehicle through which we can get more intelligent accountability," he told heads at the association's annual conference in Birmingham.
"The present system of accountability is not satisfactory, it is overburdening, there are too many bits and pieces."
He said it was important for ASCL to get involved in the debate over report cards, so that it would be something by which schools and heads were happy to be measured.
He said that, in an age of internet comparison websites, schools had to accept that parents wanted easy access to information on performance.
"The world of accountability is moving forward very fast
faster than it's ever done. That world is out there."
Dr Dunford said report cards would alter the way in which inspections were carried out by the education watchdog, Ofsted, allowing inspectors to "get into the more human side of education".
"A lot of the time inspectors spend in schools is spent poring over data with the head teachers," he said.
"That will no longer be necessary. They could focus on the quality of learning and the wider pupil experience within the school, out-of-school activities and the richness of the school experience."
Senior government adviser Professor Tim Brighouse said he was concerned that schools currently worked in an environment of high accountability and low trust.
He said a report card that was detailed and interesting to readers could help raise trust in schools.
"I'm in favour of a balanced score card," he told head teachers in Birmingham.
"The existing system of accountability is simple, is easily understood and very, very misleading.
"We need a coherent approach. We've got an incoherent, damaging approach now."
But he urged head teachers to insist that the cards were based on three-year rolling averages of schools' performance, rather than on one year's data.
Dr Dunford said it was likely that school report cards would be trialled and introduced in 2011.