New Government measures to reduce knife crime are seen as "ineffective window dressing" by defence lawyer Barry Hart.
Justice Minister Simon Power has announced a range of measures, including raising the maximum sentence for possession of an offensive weapon from two to three years in prison.
Voluntary agreements will also be arranged to limit the knives sold to young people.
However, Mr Hart says teenagers can easily ask older friends to buy them. He says young people do not think about a resulting jail term when they commit a crime.
Mr Hart says he supports plans to have police education officers in schools provide information about the dangers of carrying knives, but says that does not go far enough.
But a member of the Youth Justice Independent Advisory Group says even a few more months in jail looks like a long time to teenagers.
Anni Watkin says the increased penalty will be complemented by education in schools about the dangers of carrying knives.
A British anti crime specialist says tougher laws will do little in New Zealand.
The Be Safe organisation set up an anti-knife education campaign in England in 1998.
Founder Kevin Everard, a former London police officer, told Morning Report that toughening penalties there reassured an anxious public, but made very little real difference.
He said educating young people proved more successful.
Labour Party leader Phil Goff says it's hard to prevent people having access to knives.
But he says it's important to send a message to young people that they should not be walking around city streets carrying knives that can be used as weapons.