Labor has vastly underestimated how much it will cost to address historic underfunding for the 800,000 NSW public school students, the state government says.
The opposition has promised to boost public school funding to 95 per cent of a key benchmark by 2025, two years earlier than planned.
The party's $400 million pledge has been independently costed.
However, Education Minister Sarah Mitchell says the plan will cost $750 million per year.
"They're already short-changing with the announcement they've made," she told reporters.
"It's not enough money. They're either being deliberately dishonest or they don't understand how school funding works."
Labor called on Ms Mitchell to release the working behind her estimates, saying its $400 million figure came from the independent Parliamentary Budget Office.
Ms Mitchell's office was contacted by AAP, but did not immediately respond to a request for clarification.
Opposition Leader Chris Minns brushed off attacks about his economic credentials.
"When it comes to debt, deficit, taxes and economic performance, any way you look at it the performance of the NSW government has been dead last or the worst in living memory," he told reporters.
The benchmark Schooling Resource Standard is used to estimate how much total government funding a school needs to meet its students' educational needs.
Created in the 2011 Gonski education review, the model seeks to have private and public students fully funded by 2029.
NSW public schools will this year receive 92 per cent of estimated funding required to meet students' needs.
The eight-point gap equates to a $1.28 billion shortfall, or $1550 per student, senior economist Adam Rorris says.
Education has been a key issue in the NSW election campaign as students and teachers return to classrooms.
Both major leaders visited schools in western Sydney on Tuesday, spruiking separate commitments to make a COVID-19 school tutoring program permanent.
The coalition said its plan would cost $173 million, while Labor estimated it would cost $200 million over two years.
Labor also backed a coalition plan for universal access to preschool for four-year-olds, while saying it could roll it out faster than 2030.
The $5.9 billion policy was the centrepiece of last year's state budget.
The 10-year program was touted as a way to get women back into the workforce sooner and tackle the gender pay gap.
