He added: "Every year for the past 25 years unions have been saying the problem has been getting worse, so it must be out of control by now. I don't believe our schools are out of control. I believe they are often safe havens in a very violent society."
Mr McLean conceded drugs were the new problem with which schools had to cope, "although they've just replaced alcohol". There was also evidence of pupils becoming more disruptive and problematic at an earlier age. But he noted that indiscipline was less of a problem among girls, in primary schools, and in denominational schools. "So it's really a school improvement issue," Mr McLean added.
He, too, warned against "demonising and stigmatising children in a way which the unionswould rightly resist when the same thing was done to 'bad' teachers".
Mr McLean also said action was being taken to tackle the issue, but this could have uncomfortable consequences. Teachers now had more support staff than ever before, which he warned could lead to the deskilling of class teachers if they took the view that "they are the experts; let them deal with it".
In Glasgow, the authorities had met union demands and removed troublemakers: in one school, 10 per cent of pupils had been removed from the register. But he added: "Is streaming by behaviour in the spirit of comprehensive education? I think not."
Politicians from the main parties, apart from the Conservatives, also endorsed the Government's social inclusion agenda, although Nicola Sturgeon, the SNP's education spokesperson, said that mainstream schools were being asked to cater for disruptive children without the considerable resources which would be spent on them if they were transferred to specialist settings.