Official Information Act documents show primary, intermediate and secondary schools made just over 179 million dollars from international students in 2019, but that dropped to 139 million last year.
11,000 foreign pupils attended primary, intermediate and secondary schools here in 2019, but that dropped to 9,100 last year.
This year's enrolment and revenue figures aren't yet available.
The Ministry of Education says the full impact of the Covid-19 and the global financial downturn are just beginning to be felt.
Next year's expected to be the lowest point for international student enrolments at New Zealand schools.
Spokeswoman Cathryn Ashley-Jones says international students who arrived before the border closures are completing their programmes, so numbers are falling.
She says with so few new students, there'll be a long-term impact on revenue.
Ashley-Jones says even once they can return, numbers will likely take considerable time to rebuild.
That's due to long recruitment, fewer education agents and marketing opportunities, and the impact of the global financial crisis on students' finances.
Secondary Principals' Association president, Vaughan Couillault agrees it could take time to rebuild.
However, he says New Zealand's done such a good job providing international education, he hopes people come flooding back in as soon as the doors are open.
Couillault expects schools to make cut-backs as more foreign pupils head home.
He says some of the international fees are spent on teaching ESOL - English for Speakers of Other Languages - but a lot of it goes towards other things.
For example, the money could be used to reduce class sizes to 18 or hire external sports coaches.
Couillault says some of the international student fees have been used to help pay for Te Reo classes at his school.
More redundancies are expected at schools next year because of a lack of international students.
Couillault says a lot of teachers lost their jobs at the end of last year, as overseas students left.
He says there could be more restructuring next year.
National says the slow Covid-19 vaccine rollout has had an impact on schools' international student revenue.
Education spokesman, Paul Goldsmith, says many schools who relied on income from overseas students are doing it tough.
But he says the broader issue is doing what we can to open up our economy, which means getting vaccinated.
He says the Government had one job to do this year - ensuring we got the vaccines as soon as possible.
Goldsmith says we're playing catch up now but the rollout's been far too slow, which has extended the pain.
He says getting the country vaccinated is the only way we'll be able to welcome international students back into the country.
Goldsmith says that's been challenging because New Zealand's had a slow vaccine rollout.
The Government says it's developed a 52 million dollar recovery plan for schools affected by the exodus of overseas students.
Ministry of Education spokeswoman, Belinda Himiona, says 20 million was given to state and integrated schools last year so they could continue teaching and caring for their remaining foreign pupils.
She says education providers have been let off the Export Education Levy until the end of 2021, and that may be suspended next year too.
The Government wants foreign students to return, but only when it's safe.
The Ministry of Education says since Covid-19 border restrictions began, two tertiary groups have been given exemptions to come here.
However, spokeswoman Belinda Himiona says the Government can't promise when international school students will be allowed back in.
She says the next academic year could be similar to this one, with no large-scale arrivals of foreign pupils.