The number of NSW public school students who do not identify with a religion surged by 13 per cent in the three years to 2018, making non-believers the fastest-growing group, ahead of Islam and Hinduism.

About 43 per cent of students did not nominate a religion last year, Department of Education figures show. They come as principal and teacher groups push for mandatory Special Religious Education (SRE) to be scrapped from high school.

The least religious primary schools in Sydney with more than 100 students were Australia Street Infants', Camdenville Public and Darlington Public. The most religious were Auburn West, Wylie Park Public and Mount Lewis Infants' schools.

Among high schools, the least religious non-specialist schools were Newtown School of Performing Arts, Sydney Secondary College (Leichhardt and Blackwattle Bay campuses) and Marrickville High. The most religious were Punchbowl Boys, Auburn Girls and Granville Boys.