More than 250 South Australian public schools closed on Monday so teachers could rally in the city as well as Whyalla, Port Lincoln and Mt Gambier.
The Australian Education Union recently rejected a 2.35 per cent annual pay rise from the government along with other changes to working conditions.
"The offer's not good enough," SA branch president Howard Spreadbury told the Adelaide rally.
"It needs to come back, be revised and we'll have another look at that and see if it's ready for acceptance."
Spreadbury said a substandard agreement would have a detrimental impact on education outcomes for students, and teachers should not have to compensate for a funding shortfall.
"We can't keep running a public education system just on your goodwill," he said.
"It requires resources and it requires commitment from the state government to invest appropriately at all levels of public education to make this state the great state."
Fulham North Primary School teacher Heather McDonald, who has worked in the public education system for more than 30 years, wants smaller class sizes and more respect for teachers.
"I am absolutely over children not having enough room to work and if we increase class sizes, particularly for the junior primaries, they're not going to have enough," she said.
"The children in our state deserve better."
She said many teachers were underpaid and exhausted but persevered for the sake of their students.
"I had two 14-hour days this week and I'm almost 60, and I can't keep doing it," she said.
"I'm here because I love my job and I love my students but we can't keep doing it like this anymore.
"We need respect and we need support to do our jobs well."