According to My School of ACARA, "NAPLAN results are reported using a scale that has an average score, across all students, of 500. The spread of scores has been set so that just over two-thirds of students' scores lie between 400 and 600 (ie standard deviation of 100). NAPLAN scores provide an indication of student achievement. They provide only one snapshot of selected aspects of what students know and can do."

However, "The ICSEA was scaled to a mean of 1000 and standard deviation of 100 for all Australian schools and each of the variables was weighted in such a way as to produce a single index that best predicts performance on the NAPLAN tests."

Note:
NAPLAN - National Assessment Program - Literacy and Numeracy
ICSEA - Index of Community Socio-educational Advantage
ACARA - Australian Curriculum, Assessment and Reporting Authority