More than 40 per cent of the 795,000 students in NSW's public schools do not list any religion on their enrolment form, according to new data that comes as parents and teachers push for an overhaul of the strict rules that leave students with "dead time" if they do not attend scripture.

All schools must set aside at least 30 minutes each week for special religious education (SRE) but the data, released under freedom of information laws, shows that in more than 50 per cent of schools, most students do not nominate a religion.

Christianity remains the main religion listed (about 45 per cent), especially on Sydney's north shore, while some schools in Sydney's west have as many as 90 per cent of students who identify with Islam.

At Banksia Road Public School, 91 per cent of students listed Islam on their enrolment form while at Bellevue Hill Public, 71 per cent students listed Judaism and at Cabramatta High, 35 per cent nominated Buddhism.