The Presbyterian minister who led an attack on the screening of a film about children with gay parents at a Sydney high school had scripture classes he oversaw at the school dramatically slashed last year, documents seen by Fairfax Media have revealed.

Gayby Baby was due to be shown at Burwood Girls High and up to 20 other schools in NSW on Friday before an extraordinary ministerial decree from NSW Education MInister Adrian Piccoli led to a statewide ban on the documentary during school hours.

Minutes from a meeting at the inner-west high school show that the leading force behind the campaign to stop the film, Mark Powell, had the special religious education (SRE) classes he oversaw cut from once a week to once a term after a school council found they were incompatible with the school community.