SHA president Judith Mullen is expected to highlight the widening gap in results between the richest and poorest students, and the growth in teenage crime.

The union sees plans to set each school a target for reducing expulsions as a potential nightmare for heads. Those targets are an attempt to stop schools dumping their problem children on each other - or on the street.

SHA wants help in developing a wider range of strategies, including more alternatives to school-based education.

“Targets will make learning more difficult for the vast majority of students,” Ms Mullen said this week. “Heads will have to prove the case for exclusion almost as if in a court of law. We want more creative intervention strategies outside the mainstream for these children. We don’t want them to go into the black hole that so many of them disappear into at the moment.”

The conference in Brighton is the first under new general secretary John Dunford. He has been credited with raising the union’s profile and putting across more directly the professional concerns of members.

Those concerns this year will inevitably include the Green Paper - heads question whether enough money is being made available, and fear they will be overwhelmed as up to 250,000 teachers rush to cross the threshold in the first year.

But they will also include pay for heads and deputies. Heads are angry that three months after the Government’s headline-grabbing award of up to 10 per cent, they still don’t know the full extent of this year’s pay rise. Most are likely to be considerably less, some as little as the 3.5 per cent they received this month as a first instalment.

Deputies too, who make up half the union’s membership, are unhappy at seeing the pay gap widen. It remains to be seen whether minister Estelle Morris will placate them when she pledges a review of deputies’ pay in her address to the conference this afternoon.