The Principals' Federation says it has legal advice that suggests schools can legally refuse to enrol a violent child.
It recently suggested schools could consider defying Education Ministry directions to enrol children who have been kicked out of other schools for violent behaviour until they were confident those children would receive sufficient support.
Federation president Perry Rush said the federation had now received preliminary legal advice that said the ministry could not direct a school to enrol a child without fully considering the impact on health and safety.
Rush said the federation would further develop the legal opinion but it did not want to get into a legal battle.
"We would be reluctant to see this have to go to court, that's not what we want. We want the Government to take seriously the challenges that principals are confronted with and that young people are experiencing," he said.
"There needs to be some resolution in order to ensure that these young people are well cared for, well supported with resources and that there are alternative pathways that might mean that the young person can be kept in education without placing at risk students."
Rush said principals were caught between the requirements of the Education Act and the Health and Safety in the Workplace Act.
He said the federation was not trying to make it easier for schools to refuse to enrol difficult children.
"What we really want is for there to be a situation where there are resources, where there are pathways within the schooling system that means we don't have to get to the point of suspending young people," he said.
"That's the sort of positive, proactive, nurturing system that caters for young people in crisis and we currently don't have that system in place."
Deputy secretary of sector enablement and support Katrina Casey said the ministry had not seen the advice the federation had received.
"If a school decides to exclude a student, that will not be a decision they've taken lightly - often the exclusion comes following a period of behaviour, and despite the attempts of the school to address the behaviour. Use of the power to direct is a very last resort and one that is used very rarely," she said.