Up to 1000 schools across NSW are being promised air-conditioners in classrooms and libraries, but the state government can't say which they'll be or when they'll get them.
Premier Gladys Berejiklian on Thursday said $500 million will be set aside in next week's budget for new units to be installed over the next five years.
Every new school and those getting upgrades will get air-conditioning from July 1, while older schools will be retrofitted based on certain criteria.
Those with an average maximum temperature higher than 30C will be prioritised, although special needs will also be considered.
Ms Berejiklian labelled it the "largest investment of its kind in NSW history", but it's unclear how schools will be chosen or over what timetable the program will be rolled out.
It comes just a few months after her government branded the opposition's proposed $300 million air-conditioning policy "full of hot air".
Labor's education spokesman Jihad Dib said the announcement was a "straight rip-off" of his party's policy.
Students have been sweating it out in hot and humid classrooms for years, he said.
"We made the announcement because we knew the difference it would make to students' learning outcomes," he told AAP.
"They rubbished it ... now they've picked it up almost line for line."
Next week's budget will also include $6 billion over the next four years to build new schools and upgrade others to help cater for the state's increasing student population.
Enrolments are expected to jump 21 per cent by 2031, according to Education Minister Rob Stokes.
Most of the money has been already announced, but the funding has been topped up to enable an extra 20 projects under the program.
New primary schools are set for Green Square, Westmead, Rhodes East, Edmondson Park and Gregory Hills in Sydney, and Murrumbateman in the southern tablelands, while a new high school will be built in Edmondson Park, with upgrades planned for Randwick Boys and Girls, Birrong Boys and Girls, and Cecil Hills High.
The government is promising 170 new and upgraded schools over the next four years under the investment program.