Tests showed pupils are now more familiar with decimals than fractions
Pupils are no better at maths now than they were 30 years ago - despite a rise in exam grades, a study suggests.
Researchers asked 3,000 11 to 14-year- olds in England to sit maths exams taken by pupils in 1976, and compared their scores with the earlier results.
Analysis suggested there was little difference between the two generations.
But among pupils from the previous generation taking O-level maths, less than a quarter gained a C or above, compared to 55% in GCSEs last year.
'Teaching to the test'
Dr Jeremy Hodgen, of King's College, London, who led the research team, suggested the disparity between unchanged ability and the increase in grades was partly down to schools' obsession with Sats results and league table positions.
He said: "There's a great deal of teaching to the test, so that in trying to increase scores, schools develop an understandable focus on the test, so there's a narrowing of the curriculum."
He also said mainstream schools today had a higher proportion of lower-achieving pupils, whereas in the 1970s many of these pupils would have been in special schools.
The researchers found some differences in the abilities of the two groups of pupils in different areas of mathematics.
Today's secondary school pupils were much more familiar with decimals than they were 30 years ago. On the other hand, fractions appeared to be much harder for today's pupils, the study suggested.
Thirty years ago, pupils would sometimes convert decimals into fractions to solve a problem, but those taking the tests now did the reverse, researchers found.
Schools Minister Diana Johnson said another independent report showed pupils in England making real progress in maths and that GCSE standards were rigorously monitored.
"We do not think that research based on tests in a small number of specific topics taken in 11 schools by 11 to 14-year-olds is a good way to judge standards in the maths GCSE - an exam which tests the full breadth of the curriculum and that is taken by older pupils from all schools in the country," she said.
"Improved mathematics attainment is down to pupils' hard work and excellent teaching. This is further reflected by the fact that more and more young people are going on to study mathematics and further mathematics at AS-level and A-level."
The research was presented at the British Educational Research Association conference in Manchester on Saturday.
Former Countdown television presenter Carol Vorderman, who is leading a Conservative task force into the subject, told BBC News that there was "no question" maths exams are easier than when she was at school.
"I've spent a lot of the last month going round a lot of university maths departments and speaking to the professors and to the students... and the term grade inflation is a term which is referenced and it is used constantly," she said.