A senior education official has warned a cross-party Stormont committee that the schools system is "unaffordable".
Education Authority (EA) chief executive Sara Long yesterday provided politicians with an overview and spoke of urgent finance issues.
The EA replaced the five former education boards almost five years ago.
Since its creation, the assembly education committee was told, it had made savings of £100 million.
But Ms Long said that even with in-year savings of £20m it was on course to overspend its budget by £30m this year.
Schools are also increasingly falling into debt, she said.
The number in the red has more than doubled since Stormont collapsed three years ago. Close to 600 schools have combined debts totalling £62.6m.
Many principals described as "intolerable" the increasing financial strain, Ms Long said.
"The system requires additional funding and support to sustain improvements that have been made on educational outcomes to date," she said.
Also appearing was EA finance director Seamus Wade who advised that 80 per cent of schools' budgets are spent on staff costs.
Mr Wade said EA was prioritising which schools needed the most support ahead of the new financial year.
In March 2018, the EA launched a new approach to schools financial planning. Each school is categorised, with `category 1a' being those with an increasing deficit of more than 5 per cent of their budget or £75,000, and falling below the minimum enrolment numbers. Last year there were 90 schools in this category.
Mr Wade said several had made cuts including reducing support staff and making teachers redundant but still had a steadily worsening financial position.
Committee chairman Chris Lyttle asked Ms Long if she agreed that the system was unaffordable.
"It is certainly unaffordable at this point yes. In terms of radical investment, it would need £400m to sustain the service as it currently is," Ms Long said.
The committee later heard that the maintenance backlog facing schools was estimated to be £400m - £90m of which is considered "critical".
Speaking afterwards, SDLP committee member Justin McNulty said he was "astonished".
"School principals are crying out for investment in our school estate, even for basic maintenance," he said.
"When I pressed the officials I was gobsmacked to learn of the scale of the backlog of works needed.
"Officials explained that those works can range from painting and redecoration works to more critical works such as rewiring or electrical works and heating improvements, to urgent health and safety works.
"School principals are telling me locally of their frustration at the length of time it takes to get what they deem as urgent works completed and have expressed concern that sometimes those works are not done at all."
Members also raised concerns about the slow pace of area-planning, transport, the rising costs of special educational needs (SEN) and delays in completing statements of SEN for children.
The EA is required to complete an assessment and statement in 26 weeks, but almost 80 per cent of new statements take longer.
