A call for strike action to bring about a one-year delay in implementing National 4 and 5 qualifications was defeated at the EIS annual general meeting last week.
After a heated debate, delegates voted 102 in favour of possible strike action, and 181 against. Supporters of the motion said there simply was not enough time to prepare for the new qualification and make sure pupils did not suffer.
"We are walking into an abyss. I can't for the life of me believe why people think all the problems have been solved," said Brian McGovern, from Renfrewshire.
But vice-president Susan Quinn reminded delegates of the recent agreement that the Scottish government would provide a support package for the senior phase.
"We called for a delay and it has been decided by the Scottish Parliament that that one-year delay will not happen. We have had two months of the package; we have to give it a chance to work," she said.
The union agreed to ballot over possible strike action if changes to teachers' conditions of service are made without the agreement of the Scottish Negotiating Committee for Teachers.
Delegates also supported possible further strike action over pension reforms and public sector expenditure cuts.
The issue of setting classes by ability split delegates, with some arguing that setting was not appropriate for subjects such as maths and others saying the mixed ability model not only fitted with comprehensive education but was even more important under Curriculum for Excellence.
Anne McCrae, an English teacher from Edinburgh, who won backing for a motion to reject the practice of setting, pointed out that it was already banned in Sweden. She was not looking for setting to be banned overnight in Scotland, but urged the EIS to be bold and not make it a "default setting" in secondary.
But Ronald Mathieson, a maths teacher from North Lanarkshire, said mixed ability had not worked in his subject and that was why setting had been reintroduced.