Most South Australian public schools will stay open during a half-day strike by teachers, indicating a lack of support for the industrial action, the state government says.
But union officials believe teachers will back the strike in big numbers, and say the action will "speak for itself".
Treasurer Rob Lucas has offered more details on the pay and conditions dispute which he says includes demands for an interim 3.5 per cent pay raise that would cost the government $80 million a year.
Mr Lucas says 692 of SA's 875 schools and preschools will stay open during Thursday morning's strike with 194 of those offering a modified program.
Only 183 schools have indicated they will close for the morning.
"Let there be no mistake, this is a resounding vote of no-confidence in the union bosses whose ill-conceived rush to strike has been shown to be puerile in the extreme,'' the treasurer said on Wednesday.
But Australian Education Union state vice president Dash Taylor Johnson said schools had been pressured to stay open and questioned what programs would be available.
"Let's let the action tomorrow speak for itself. Let's have a look at what happens," he said.
"We'll really see the strength of educators and why this is important for them in trying to maximise outcomes for students."
Thursday's strike will be the first by SA teachers in about 10 years and comes after a vote of AEU members overwhelmingly endorsed the action and the call for the government to resume negotiations.
The union says it wants reduced class sizes, more support for country schools and more resources for special needs children among other changes.
But as well as the annual pay increase, the government says teachers are seeking extra salary increases to address the gender pay gap, more sick leave and more non-contact time with students for report writing and collaboration with their peers.
Mr Lucas said parents, grandparents and many teachers recognised the government was delivering a record investment in education and there was no "plausible, logical or rational reason in the world" for strike action.
