"It is clear from the research that the extra spending is simply not delivering value for money," Geoff Mawdsley, director of Reform Scotland, said. "Put another way, billions of pounds have been spent in the last decade to little or no effect."
While spending per pupil has risen from £2,092 to £4,638 at primary level and from £3,194 to £6,326 at secondary schools, the proportion of those gaining five good grades at the end of fourth year has fallen from 47 per cent to 46 per cent.
Reform Scotland also claimed that data it had obtained showed that pupils in England who had been lagging behind Scotland in 1998 are now ahead, with the number achieving equivalent grades rising from 36 per cent to 48 per cent.
The Scottish education system has long been regarded as among the best in the world, but the report claims that this view is now a myth.
Mr Mawdsley called on the Scottish government to publish more information about pupils' performance. "Using the measure of the pupils attaining five good grades by S4, including maths and English, would be a good start," he said.
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