All local authorities in Wales should provide behaviour support services, including pupil referral units, to help schools manage disruptive children, but not all do, according to David Evans, who takes over as secretary of the National Union of Teachers Cymru next month.
Union members, meeting in Cardiff last week, were also told the Education and Inspections Bill before Parliament should give them clearer rights to discipline pupils and confiscate property.
Mr Evans said: "We want a PRU in every area, stronger powers to exclude those who willfuly persist in disruption, and training in behaviour management. We want teachers to have defined what they can and can't do, and we need national guidelines on the issue of restraint."
Neil Foden, head of Ysgol Friars, Bangor, said one LEA deemed expulsion "inappropriate" for pulling a knife on another pupil. "A lot of our authorities are too small and lack adequate resources to provide consistent support to schools," he said.