The Welsh Government has told secondary schools they must not allow newly published league tables to distract them from the goal of improving standards and performance.
Statistics published by the BBC last week, after a Freedom of Information request, revealed the value-added scores of Wales's secondary schools and variability in their GCSE performance and ranked them accordingly.
The Government said the tables were "extremely simplistic", while educationalists said they were unhelpful and not in the best interests of teachers, students or communities.
In a letter to heads and other education authorities seen by TES Cymru, Chris Tweedale, director of the Government's children, young people and school effectiveness group, said the BBC's publication could lead to information being used in a manner contrary to Government policy.
He said it was education minister Leighton Andrews' view that "simplistic league tables have no role in the improvement agenda for Wales".
Mr Tweedale added: "They can be divisive and misleading and do not in themselves promote improvement."
The Welsh Government scrapped secondary school league tables in 2001, saying they were not supported by teachers or parents.
But a report from Bristol University last year said the move had "reduced school effectiveness" by two GCSE grades per pupil. Since then the poor Programme for International Student Assessment (Pisa) results and a critical report from inspectorate Estyn have focused the agenda on improving school standards.
In a major speech in February, Mr Andrews said the "robust use of data" would play an important part in driving improvement. He announced the introduction of banding for schools and the formation of a new school standards unit.
Teaching unions were united in condemning the BBC's publication. NASUWT general secretary Chris Keates called it a "reckless and irresponsible exercise" that will have done "untold damage to the morale and motivation of teachers".
ASCL Cymru secretary Gareth Jones said: "Using such data to name and shame certain institutions or individuals does not work."