School suspensions have risen by more than a third over the past six years but do little to improve the behaviour of children, research has found.
The study, conducted by Uniting Care, has led to calls on the NSW government to review its education policy and allow for more in-school suspensions.
Analysis of NSW Department of Education figures shows the number of long-term suspensions - lasting five to 20 days - has increased by 36 per cent in six years. Suspensions increased from 12,326 in 2006 to 16,814 last year.
A quarter of students were placed on long suspensions more than once last year.
Physical violence was the reason for 40 per cent of long suspensions and 47 per cent were for persistent misbehaviour.
Karen Bevan, from Uniting Care, who oversaw the research, said she found no evidence that suspension improved children's behaviour.
The research, to be presented next week at the Joint Australian Association for Research in Education Conference, found disadvantaged children in particular fell behind in their school work after taking as much as five weeks off school in one year after repeated suspensions.
''Suspension doesn't work because it doesn't teach you anything,'' Ms Bevan said.
''Some students were suspended for more than 2½ weeks out of a 40-week school year. If you get more than one long suspension, you are looking at five weeks a year. That's a long time to be off school.''
Ms Bevan said the figures showed that Aboriginal children made up 23 per cent of those suspended for long periods.
''What does work is where you run the suspension in school,'' she said. ''There is evidence internationally that is a more effective way of keeping kids connected with education.''
A NSW Department of Education spokesman said the department operated 22 suspension centres attached to schools.
He said suspension centres aimed to provide skill development opportunities and support for students to help them re-engage at school. He added that schools were required to give students on long suspension a school work plan and the students were expected to complete that work.
Raising the school leaving age to 17 in 2010 has contributed to an increase in disruptive behaviour, according to a report by the NSW Auditor-General, Peter Achterstraat. This month Mr Achterstraat said that since the leaving age was increased, some year 11 students who may otherwise have left school were disruptive, wasting teachers' time or truanting.
Ms Bevan said her organisation was concerned about the 27 per cent of students who were re-suspended on long suspensions.
''Our research tells us that group of students are of serious concern and likely to be the students who most benefit from engagement in education,'' she said.
The NSW Department of Education spokesman said schools had a duty of care to protect students, teachers and other staff from violent students and those involved in criminal activity.
''Suspension is not intended as a punishment,'' the spokesman said. ''Suspension is only one strategy to manage inappropriate student behaviour within a school's student welfare and discipline policies.''
Ms Bevan said the former Labor government toughened school suspension policies over the period their use increased.
''A real concern for us now is that the cuts to education announced by the O'Farrell government may reduce support services further and we could see an increase in suspensions again,'' she said.