Their finding will give Scottish ministers further reason to consider their strong support for setting, reinforced in the response to the National Debate on Education.
"If governments wish to change practices in schools, it seems that exhortation alone will not suffice," Susan Hallam, the chief researcher, says.
As in Scotland, ministers and their advisers have pressed hard for the past six years for schools to introduce setting.
But the London researchers suggest teachers want hard evidence first.
Even in maths, in which setting was most prevalent, only 24 per cent of same-age classes and 39 per cent of mixed-age classes in upper primary used setting, based on a study in 800 schools in 1999.