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More children experiencing ''serious adjustment issues'' over split families or being put into care is believed to be contributing to an increase in schools having to discipline them for bad behaviour.
The number of suspensions of Otago pupils for physical assaults on other pupils reached 28 last year - double the number in 2016 - and assaults on staff have increased 70% to 17 over the same timeframe.
Assault is just one of the bad behaviours that has caused an overall increase in the number of disciplinary actions handed down to pupils in southern schools.
And one principal said the numbers were likely to continue rising before they improved.
Ministry of Education data, released under the Official Information Act, shows the number of stand-downs in Otago schools rose 13.1% to 814 between 2016 and 2017, suspensions rose 39.6% to 187, exclusions rose 72.7% to 57, and expulsions increased from fewer than five to seven.
In Southland schools, stand-downs increased 21.1% to 613, suspensions increased 11.4% to 98, exclusions rose 39.3% to 39, and expulsions remained stable on fewer than 5.
Data for 2018 is not yet available, but the numbers appear to have been rising year on year over the past decade.
The disciplinary actions were handed out for a range of incidents, including drugs, alcohol, arson, continual disobedience, sexual misbehaviour, the use of weapons, and verbal and physical assaults on fellow pupils and teachers.
Otago Secondary Principals Association secretary Gavin Kidd believed the increase was partly caused by changes in the pupils' social environment.
''I believe there are more kids experiencing issues over split families or going into care, and many schools are having to take a much greater role in providing social support and mental health support than they used to.
''There are increasing numbers of students who have got serious adjustment issues.''
However, he also said disciplinary actions may be increasing because schools were becoming less tolerant of bad behaviour.
Logan Park High School co-principal Kristan Mouat agreed.
She believed schools had evolved and were more focused on their responsibility to provide safe environments for pupils to learn and express themselves, and a safe environment for staff to work.
She said 10 years ago, if there was a fight on school grounds, it was accepted by many schools as just ''boys being boys''.
But schools were now less tolerant of bad behaviour - particularly physical assault, bullying and cyber bullying.
''There's a lot of research and evidence showing this kind of behaviour is very damaging, so we need to have clear expectations and clear consequences.
''I would imagine that schools are trying to send a clear message to students that there will be consequences for their actions.
''That will be feeding into it [the increase].''
She said the slowly-changing school environment meant pupils were now more comfortable informing staff of unacceptable behaviour.
She believed the statistics may continue to grow before they declined - particularly around more recently identified misbehaviour like cyber bullying - because it would take time to stamp out.
Ministry of Education sector enablement and support deputy secretary Katrina Casey said the number of disciplinary actions handed down by schools should not be used as a ''proxy measure'' for total student behaviour.
''It's important to note that stand-downs, suspensions, exclusions and expulsions are measures of a school's reaction to the behaviour.
''While one school may opt to suspend a student over a particular incident, another school may not.''
She said schools had developed comprehensive, local approaches to promoting pro-social behaviour and wellbeing within their setting.
''We support these efforts, and the development of whole school capability, with programmes such as Positive Behaviour for Learning (PB4L).
''We also provide bullying prevention guidance for schools.''
Guidelines for physically restraining pupils exhibiting difficult behaviour have also been developed to help school staff, she said.