Many local authorities have admitted they do not want to introduce faculty heads in secondaries, Ian Wishart, East Lothian, said.
The NASUWT had received responses from 18 authorities, eight of which did not want faculties, although they were well established in the Western Isles and Shetland.
"Some authorities are doing it on a school by school basis and others are applying it across the board," Mr Wishart said.
Ian McCubbin, Perth and Kinross, said that his authority opted not to introduce faculties after all 10 secondaries objected.
"In particular, larger schools have larger departmental teams and generally see no reason to move to a faculty arrangement. In larger departments such as English and mathematics, some headteachers are considering appointing PT resource for implementing literacy and numeracy across the curriculum."
But others challenged the commonly held view about the failure of faculties. Fiona Rowland, a faculty head in West Lothian, said that with a half-time teaching commitment she could give support to subject leaders and class teachers, especially on discipline.
"What is evolving in West Lothian is not bad, but it's not what they intended," she said. Her school had 1,000 pupils, and six faculty heads had been appointed where there would never have been six assistant headteachers.
Tom Noon, a Glasgow faculty head, said the structure should be given a chance, particularly in science. It had a common course in S1 and S2, although there were differences further up the school. "But faculties in, for instance, home economics and PE are a bit of a farce," Mr Noon said.