The public funding for some of Sydney's most expensive private schools has increased at twice the rate of many of the state's poorest schools, new analysis of the latest MySchool data reveals.

Trevor Cobbold, a former economist for the Australian Productivity Commission and convener of the Save Our Schools public education advocacy group, analysed the data and found the average funding increase per student for 14 selected private schools was 23 per cent from 2009 to 2013.

For 15 of the most disadvantaged public schools in NSW the average increase per student was 11 per cent over the same period, the report says.

"In NSW, government funding for Meriden School increased by 29 per cent; Ravenswood by 28 per cent; St Andrew's Cathedral School by 26 per cent; and for Ascham, Kincoppal Rose Bay, The King's School and Trinity Grammar by 24 per cent," the report says.