The Secondary Principals' Association says it would take a number of prosecutions to convince teenagers cyber-bullying was a crime.
The Law Commission is recommending a major legal shake-up to criminalise cyber-bullying, inciting suicide and the publishing of intimate videos without consent.
It has suggested a new offence be created to combat grossly offensive, indecent, obscene or menacing digital communication.
Secondary Principals' Association president Patrick Walsh says making cyber-bulling a criminal offence would be great for schools at their wits ends with how to deal with the problem.
But he says it runs the risk of making teenagers accidental criminals, because they won't understand the seriousness of the crime.
Mr Walsh says before any legislation was signed off, global internet giants like Twitter and Facebook would have to commit to any law.
He says there would also have to be discussion to determine whether there should be separate penalties for youth and adult offenders.
The Human Rights Commission says bullies will be limited in any claims they make about freedom of speech if cyber-bullying laws come into force.
Chief Commissioner David Rutherford supports the proposal to make cyber-bullying a criminal offence.
He says bullies need to know the right to life and personal security are considered equally as important as the defence of freedom of speech.
Legislation 'for digital age'
The Law Commission recommends the Harassment Act, Human Rights Act, Privacy Act and Crimes Act be updated for the digital age.
Commissioner Professor John Burrows says measures on cyber-bullying should be enshrined in the Summary Offences Act.
"If a communication is grossly offensive, was intended to cause substantial hurt and did in fact do so, then that could be a criminal offence.
"We wouldn't expect that to be used very often at all, but the fact you've got something there at the end of the line is an indication that this kind of conduct is not approved by society."
The commission also wants a communications tribunal set up to issue cease-and-desist notices, and all schools forced by law to implement effective anti-bullying programmes.
The proposals are contained a ministerial briefing paper released on Wednesday.
Justice Minister Judith Collins is supporting the proposal, which is expected to go before Parliament at the end of the year.