They say the Index of Community Socio-Educational Advantage, a measure used to define statistically similar schools, fails to take into account the unique circumstances of the Parramatta/Holroyd area.

Variables comprising the index include socio-economic characteristics of the areas where students live, whether a school is in a regional or remote area and the proportion of indigenous students enrolled.

Local public high school principal Lila Mularczyk, who is also deputy president of the NSW Secondary Principals' Council, said the website had ``arbitrarily clustered statistically similar schools together''.

``In one statistically similar group you can have a single-gender suburban high school rated against a primary school in a rural area compared against an exclusive private school across three different states,'' she said.

Principal Patricia Baker, of Cerdon College, said the measure was crude because it did not take into account the students' proficiency in English.

``The new index does not account for the language of both students and parents,'' she said. ``New arrivals [to Australia] are being ranked against students who've had 13 years experience in speaking English.''

Holroyd High principal Dorothy Hoddinott said she was ``very cranky'' with the system.

``It's a lot of rubbish,'' she said. ``The average score in this school is low because so many students are doing the tests after just arriving in Australia. And 34per cent of our students have been here less than three years. Leaving out this information [from the index] produces a bias when interpreting it.

``It flies in the face of multiculturalism.''

Ms Hoddinott said the key performance indicator for schools should be their HSC results.

``Low socio-economic schools average only 15per cent of their students reaching university,'' she said.

``Last year we had 48per cent of ours accepted in first offers. We're sending more children to university than go from many middle class schools.''