The coalition has promised an additional $50 million to NSW private schools if it wins the state election at the weekend.
Costings published by the Parliamentary Budget Office this week show the coalition proposes spending $50m on grants to Catholic and non-government schools in the 2023/24 financial year.
The cash would help those schools build new infrastructure and be allocated based on need.
Education Minister Sarah Mitchell said private schools were vital to the state's education sector, and the funds would be targeted to areas of "high need".
"The non-government school sector plays an important role alongside our public schools in supporting the education of NSW students," she told AAP.
"Therefore alongside our additional $1.2 billion committed on top of our $8.6 billion investment in new and upgraded public schools, $50 million has been allocated to capital works projects at low-fee non-government schools, targeting areas of high growth and need to accommodate additional students."
The funds would be allocated over 2023/24 through the Building Grants Assistance Scheme.
The parliamentary budget office said the coalition would fund the scheme from existing Department of Education resources, and it considered the additional funds "business as usual".
It comes after figures from the education department showed the number of demountables used as classrooms spiked to 5903 in April last year.
NSW Teachers Federation president Angelo Gavrielatos said the number of demountables has grown by one-third since the coalition took office in 2011.
The costings also revealed NSW Labor had committed $60m over four years to expand kindergarten access in NSW private schools, in funds it planned to allocate off from the government's $1.4b universal pre-kindergarten scheme.
