The Secondary Principals Association says schools will be running against the tide of public opinion if they heed fresh calls to avoid expelling their most troubled students.
Principal Youth Court Judge Andrew Becroft has called on schools to keep troubled children enrolled as long as possible so they are less likely to become criminals.
The association agrees that is a good idea and would save the country money in the long term.
But association president Patrick Walsh says it might be difficult in the face of hardening public attitudes to the way schools deal with student misbehaviour.
Mr Walsh says people increasingly want schools to expel bullies and drug dealers rather than try to rehabilitate them.
The association has told principals they might be challenged if people think they have taken a soft approach.
It also says schools do not have enough resources to work with the most difficult students.
Mr Walsh says schools might require a student to have drug or behaviour counselling but they are often told that there is a long waiting list or someone has to pay.
Children's Commissioner Russell Wills says families need an appeals system set up so they can challenge schools that try to expel or suspend their children.
Schools at front line - judge
Judge Becroft says school boards of trustees should act as front-line fighters against youth crime.
He says three quarters of all youth offenders are not in school, because they have either been expelled or suspended, or have slipped through the system.
Judge Becroft says boards of trustees are sometimes too ready to exclude problem students, which only shifts their behaviour into the wider community.
He says ideally schools should act as hubs for social support services so resources can be targeted at students who are most at risk.
But, he says, the Ministry of Education believes schools need to better manage the resources they have.