Mr Dalziel identified children with emotional and behavioural difficulties as the most problematic in a mainstream setting. "At the very extreme end of EBD, maybe the only long-term solution is to accept that an awful lot more resources have to be diverted from the teenage end of the market to the younger end of the market," he said.
"Maybe we have to accept in the secondary world that we should be encouraging politicians and officials to divert more resources into earlier stages where they can do the most effective work. They might not cure everything but they have a better chance of success."
Mr Dalziel pointed to the success of Glasgow's investment in nurture groups (which target pupils entering P1 with emotional, behavioural or developmental problems) and the employment of play therapists to work with pre-five and early years groups, teaching them how to share and how to recognise the impact of their behaviour on other people.
He believed mainstreaming could work provided the will was there and there were sufficient resources and full support for children, families and teachers. But Mr Dalziel conceded: "It may be that mainstream is not the ideal place for a teacher to find adequate support."
He concluded: "At the end of the day there are limits and people have to recognise that."