New research has found private schools provide a major academic boost for secondary students even after their background and prior school achievement was factored in.
The "value-add" of an independent school was worth an average eight points on a student's Australian Tertiary Admission Rank, challenging a recent review which said socio-economic status – not the school sector – was the main decider of academic success.
The findings have been embraced by the ACT's independent schools association a week after celebrated author Mem Fox launched a stinging attack on the claimed "confidence trick" played on parents by private schools.
University of Melbourne adjunct professor Gary Marks' analysis of the results of the more than 40,000 Victorian students' who obtained an ATAR in 2011 revealed Catholic schools averaged six ranks higher than government school students, and independent schools eight higher, when scores were controlled for socioeconomic status, achievement in the Year 9 NAPLAN tests, gender and language background.
Association of Independent Schools in the ACT executive director Andrew Wrigley said the research, published online by the Australian Journal of Education on Monday, undermined Fox's argument non-government schools failed to add the value for students which would justify their higher fees.
"Independent schools are rightly proud of their academic achievements," he said.
"If they weren't delivering on what they said they would, and what parents were seeking, then parents would vote with their feet."
Dr Marks' research found students who moved from the government to the independent sector between years 9 and 12 obtained 8 ATARs higher than students who remained in the government sector, even when SES and Year 9 NAPLAN performance was factored in.
Mr Wrigley, who spent nine years teaching in government high schools and 16 in non-government schools, said Fox's criticism of the level of federal funding for private schools did not adequately acknowledge the scale of state and territory funding to public schools.
""The Productivity Commission report last year put the differential of ACT government funding between government and non-government schools as nearly $13,000 per student," he said.
He said independent schools were up front about the culture and expectations they had and parents who chose these schools did so for a range of valid reasons, including reputation and values, a single sex or co-ed environment, and religious preference.
Save Our Schools convenor Trevor Cobbold, a retired economist, said the research was "out of kilter" with the overwhelming evidence from international studies and about 30 Australian studies in the last 15 years which found little difference between private and public school results once SES was factored in.
"[Dr] Marks' modelling under-estimates the impact of socio-economic status on the comparative results of public and private schools because it ignores the impact of school SES and because using prior achievement as a control dilutes the impact of student SES," he said.
Dr Marks, who has been published internationally, said school SES was a "statistical artefact" and it was well established in the academic literature that prior achievement was the most powerful influence on students' educational outcomes and was highly correlated with cognitive ability.
The ACT government will spend about $10 on public schools for every $1 it spends on non-government schools in 2015-16.
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