Parents are often of little help to teachers trying to deal with badly behaved students, according to a survey.
The survey by the Council for Educational Research found that one in five teachers say they get little or no back-up from school management.
The survey of 750 secondary teachers in Wellington and Hutt Valley schools found that a third of teachers feel working with parents to improve behaviour is poor or does not happen.
It also found more than 60% of teachers have had one or more students leave their class this year because of severe behavioural problems.
These include physical attacks on teachers or other students, verbal abuse, damage to property and students attending class under the influence of drugs.