Hundreds of schools across South Australia have been affected as teachers walked off the job, marching on state parliament to demand better pay and conditions.
The government told parents at 167 public schools to make alternative arrangements for their children on Friday.
A further 152 schools operated with a modified program, while the state's remaining 608 schools were open as normal.
The Australian Education Union said 80 per cent of its members voted in favour of the strike after the government's "insulting" three per cent pay rise offer.
"Every day, over 35,000 South Australian students are going without a consistent teacher. It is a crisis affecting schools and preschools right across our state," SA union president Andrew Gohl said.
As well as a larger pay rise, the union is demanding the government ease workplace pressures by cutting instructional time by 20 per cent.
Thousands of teachers and supporters gathered at South Australia's parliament in protest of their pay and conditions on Friday.
Many brandished signs with messages including "the last straw", "save our schools", "schools just wanna have funds" and "teachers unite for learning rights".
Teachers derided the pay rise offer and said pressure on them was rising.
"We're overworked, we're underpaid, we need more support in the classroom," one teacher told the ABC.
"We have a huge number of children and young people with exceptional needs, and we want to be able to support them effectively."
Education Minister Blair Boyer says the state budget can't afford the reduction in instructional time, which would equate to a billion dollars extra per year on top of the wage claim.
"We have to find meaningful workload reduction that doesn't mean kids in South Australian classrooms get a poorer quality education," he said.
"You've got two options: you've got kids have less education, or you backfill those teachers.
"You've got to find the staff and you've got to pay them. That's where the cost comes from."
Mr Boyer believes negotiations are on the right track after the union dropped its demand for a school support officer in every classroom.
"Today's meeting was positive, there's no doubt about that," he said after meeting with teachers on Wednesday.
"I thought we made more ground than we've made at a lot of meetings that we've had.
"It's not muskets at dawn or anything like that, we are talking to each other and negotiating in good faith."
The education department had urged parents to check the status of their child's school before sending them off on Friday, but there were provisions for some staff to be at closed schools to make sure any children unexpectedly dropped off were safe.
To add to Friday's disruption, trams did not run before the morning peak as drivers went on strike over a pay and conditions dispute of their own.