Key stage 2 pupils' scores under teacher assessment improved more slowly than did their test results in the years 1996-2000, the first detailed analysis of assessment scores in these years has shown.
The proportion of pupils achieving level 4 in the English tests increased by 17 percentage points, from 58 to 75 per cent. But under teacher assessment the rise was only 10 points, from 60 to 70 per cent.
In maths, test scores rose 18 points, from 54 to 72 per cent. Teacher assessment scores improved only 12 points, from 60 to 72 per cent.
Professor Colin Richards, of St Martin's college, Lancaster, who carried out the analysis for the Association of Teachers and Lecturers, said the figures added further weight to the argument that primary improvements had been overstated.
The results come as the Department for Education and Skills is embroiled in a row with the Statistics Commission over the degree to which standards have improved in primaries.
Professor Richards also looked at inspection data from the Office for Standards in Education and the evidence of several research studies in seeking to ascertain whether standards had risen.
His 27-page report said the evidence suggested that there had been improvements between 1995 and 2001 in English, maths and science, but that this had not been as great as the increased test scores implied.