In fact, inclusion may raise overall attainment, although the evidence remains limited, one of the Britain’s leading researchers on inclusion, told a conference in Dundee yesterday (Thursday).

Professor Alan Dyson, co-director of the special needs research centre at Newcastle University, acknowledged a lack of convincing evidence but insisted that available research shows “no conclusive evidence of negative effects”.

He said: “The basic message is that if you had to make a policy decision, your policy decision would be pro-inclusion . . . overall you get a modestly positive effect in academic and social outcomes.”

Professor Dyson accepted there was often a contradiction between increasing the inclusiveness of a school and raising the attainment of its pupils but claimed the reality was more complex and that there was no reason why the two aims should be in conflict.

Even including children with behavioural difficulties appears to be “mildly positive” based on small-scale, mainly American studies.

“If you turned the argument on its head, there is no conclusive evidence at all for putting kids in special schools,” Professor Dyson said.

The conference, which was organised by the Scottish Schools Ethos Network, heard that opinion on inclusion is split. Some teachers claim that discipline is slipping because there are more pupils with social, emotional and behavioural difficulties and others counter that having an SEN child in the class develops caring skills.

Professor Dyson accepted that reconciling inclusion and attainment was not straightforward “but it does at least seem to be possible and desirable”.

One of Scotland’s leading researchers, Gwynedd Lloyd of Edinburgh University, appealed to teachers not to reject social inclusion “on grounds that are based on myths”.

“One of them is that social inclusion means that all children with behavioural difficulties are in mainstream and it is clearly not the case.

Paradoxically, there are probably more children educated outwith,” Dr Lloyd said.

In practice, the policies initiated by ministers had removed many difficult pupils from classes and placed them in out-of-school provision, units and support bases.

In 1993, 1 per cent of pupils were in special schools and that figure rose to 1.1 per cent in 2001. Pupils with severe and complex difficulties and with social, emotional and behavioural difficulties remained largely in special provision.

Excluded pupils were likely to be disproportionately poor, looked-after or with special educational needs. Pupils more likely to be in mainstream were those who had physical disabilities or sensory impairments.