The Australian Education Union report ending the capital funding divide in Australia's schools calls for the federal government to put more funding forward for upgrades to public schools.

National president Correna Haythorpe said federal funding for public school capital works ended under the Turnbull government in 2017 and should be restored.

"Right now, it's public schools that have been denied that capital funding ... the funding that they need to provide for enrolment growth, for building maintenance, for building new, state-of-the-art facilities, and that needs to change," Ms Haythorpe said.

Education Minister Jason Clare said the government was investing in public schools through the $215.8 million schools upgrade fund.

"From upgrading art rooms and tech rooms to new outdoor equipment and replacing demountables, this funding will deliver upgrades to public schools that need it the most," he said.

A 2023 union survey found that one in five principals did not have adequate classrooms to meet current demand, while two in five did not believe they had the infrastructure to meet enrolment growth over the next five years.

The report calls for a $1.25 billion injection of capital funding from the federal government as well as an ongoing fund in line with investment in private schools.

Ms Haythorpe said demountable classrooms often became permanent fixtures in public schools.

"Teachers and students in public schools actually deserve the best quality teaching and learning spaces. But we know that that's not the reality for many across the nation."