Underachievers make better progress when taught alongside their peers.
Pupils who are falling behind do better when taught with the entire class than when taken aside for individual tuition, according to Jonathan Solity, of University College London.
The TES last week reported that Gordon Brown has pledged to spend pound;35 million a year on one-to-one tuition so that by 2011 at least 30,000 7-year-olds should be receiving individual maths teaching through the Every Child Counts initiative.
However, Dr Solity said: "Whenever anyone fails, we automatically give them one-to-one teaching. But in Britain we are still bedevilled by a long tail of underachievement. So whatever we have been trying isn't working."
He spent two years working with key stage 2 pupils. In one class, the lowest-achieving pupils were given one-to-one teaching. In the other, they were taught with the entire class. He observed the pupils for 21 months, from the beginning of Year 5 to the end of Year 6.
On average, the pupils given one-to-one tuition made 20 months' progress. But those who were taught with the rest of the class advanced by 29 months.
One child entered Year 5 42 months behind his age group. By the end of Year 6, after two years of whole-class teaching, he was just 15 months behind, a progression of 27 months.
Dr Solity believes that the difference is partly because one-to-one sessions are often led by teaching assistants or parents rather than by qualified teachers. He believes working alongside more able pupils is the best way for underachievers to learn. He draws a parallel with an amateur tennis player watching Wimbledon: "If you don't watch Wimbledon, you have no idea what good tennis looks like or what to aspire to," he said. And taking pupils out of the main class gives them an "underachieving" label that lasts throughout their school career.
Encouraging all pupils to work together in small groups enables higher achievers to show less able classmates what they are aspiring to. Teachers can then approach each group individually and check that all pupils understand what they are supposed to be learning.
"The whole class is given the same message: you are getting better," said Dr Solity. "The fact that some remain behind their peers doesn't seem to matter - as long as they're all doing better than they were."