Government funding of public school facilities is about one third the amount spent by the private school system - a difference of $8.4 billion.
The findings are contained in the report, Rebuilding Public Schools: Investment Targets for 2020, commissioned by the Australian Education Union, The Australian newspaper reports.
Independent education economist Adam Rorris, analysed capital expenditure between 2002 and 2005 - the latest years for which private school finances is available.
He found the average amount spent by private schools rose from $1,380 to $1,560 per student - up $180 in 2008 dollars - over the three years.
Spending by state and territory governments went from $537 to $542 per student - up $5.
The largest differences were in NSW, Victoria and Queensland, which have funding gaps of about $3 billion, $2 billion and $1.5 billion respectively.