Secondary maths teachers are failing to adapt their teaching methods to the demands of A Curriculum for Excellence - with the result that pupils' attainment, enjoyment and confidence are plummeting compared with early primary.
The latest report on 5-14 attainment from the Scottish Survey of Achievement, published this week, shows secondary teachers still often fall back on "chalk and talk" lessons involving more textbooks, less discussion and more whole-class teaching than in primaries.
The survey also questions teachers' judgments on pupils' progress.
The proportion of pupils reaching the expected standards in maths falls from 85 per cent at P3 to 30 per cent at S2; those at expected numeracy levels drop from 90 per cent to 45 per cent in the same period.
Education Secretary Fiona Hyslop said the declining performance at S2 justified the Scottish Government's decision to focus on early intervention. She suggested that A Curriculum for Excellence would "reinvigorate" maths by making all teachers responsible for numeracy.
She said the new curriculum was already motivating children and helping them enjoy maths, which "can only translate into higher levels of attainment in the future".
Ronnie Smith, general secretary of the Educational Institute for Scotland, said ACfE would give teachers more freedom to make maths and numeracy "more relevant and engaging".
But it seems secondary teachers are toiling to adapt to A Curriculum for Excellence. While about 25 per cent of primary teachers are "not at all satisfied" with support relating to the new curriculum, the figure jumps close to 40 per cent for secondary teachers, the report says.
The SSA report suggests there has been no improvement in numeracy levels since 2005, and they may even have dropped. It follows the Trends in Mathematics and Science Study findings in December, which showed Scotland's P5 and S2 performance in maths and science ranked alongside Third World countries.
The SSA scrutinises a different aspect of the school curriculum each year. The report on maths followed a survey of 40,000 pupils in P3, P5, P7 and S2 in 1,200 schools, which was carried out in May 2008.
It shows that attainment levels, as well as pupils' enjoyment of and confidence in maths, all fall in S2, even though most want to do well in the subject and 95 per cent believe it is useful.
Primary teachers' lessons were enjoyed by far more pupils, even though the teachers were less confident than secondary staff and one in five had not taken part in any maths-related professional development in the previous four years. About two-thirds of P3 found maths interesting and enjoyable "very often"; this fell to less than 20 per cent by S2.
As they moved from P3 to S2, pupils reported being taught more often as a class, using textbooks and writing in jotters. Pupils and teachers agreed that teaching as a whole class was more common in S2 than in primary.
Between P7 and S2, the number of pupils who "hardly ever" get to discuss their ideas almost doubles. The proportion saying they "very often" discuss with their teacher what they are going to learn remains steady through primary at about 60 per cent, before dropping to about 40 per cent in S2.
More S2 pupils report being asked to explain answers "very often", more than at any primary stage.
Teachers appear to have an inflated sense of pupils' progress in maths which becomes most pronounced at S2: more than 60 per cent of pupils are at or above expected levels, say teachers, while the survey calculates the number at 30 per cent.
Pupils' assessment of their own abilities is less upbeat: at P3, more than three-quarters rate themselves above average, but this falls to less than half by S2.
But Mr Smith and Ms Hyslop said Scotland continued to perform well in upper secondary.