High school teachers say increasing numbers of students are getting addicted to online video games and some are failing classes as a result.
Many teachers say boys especially are spending day and night playing or thinking about games and often become aggressive when their parents try to stop them.
Wellington College principal Roger Moses says some students stay up all night playing games and if they do make it to school the next day they're too exhausted to learn.
Mr Moses says some are failing, becoming depressed and dropping out of sports to play online.
Nayland College information technology teacher Craig Nicoll, of Nelson, says he is seeing a similar problem emerging among students there.
He says it usually starts when they begin secondary school and struggle to make friends.