A special education centre lauded as being at the pinnacle of its sector is to lose funding for its therapists in a decision that will have "horrific" consequences for its children.

The National-led Government has decided the country can no longer afford $2.5 million a year to fund therapy services for hundreds of children like Trey Hess, who was born with achondroplasia (dwarfism) and hemiplegia (paralyses) of his left side.

Trey needs a specialised chair, a power wheelchair, an adapted computer mouse and splints on his left limbs when he is at school.

He also needs weekly speech and language and occupational therapy and daily physiotherapy. In the first term of this year, he received 44 hours of one-on-one interventions.

Staff at the Endeavour Centre at Mt Roskill Primary School, which Trey attends, say they are distraught at the decision.

The regular therapy is a relief for Trey's mother, Peti Ellis, who has battled for support since he was born. She has watched his breadth of movement, recovery from major operations and academic ability improve "immensely", and is devastated that the loss of therapists will stall his progress.

The Endeavour Centre has 34 children with high and very high needs. Manager Jill Gilberd said the cuts would be "horrific".

Last year, she said, the Ministry of Education paraded OECD representatives through the centre to showcase New Zealand's leading approach to special-needs education.

But "the whole concept of the place is not going to be able to work" if it loses two therapists next year.

Ms Gilberd said therapies would need to be strictly prioritised, and pupils with lesser but nonetheless significant needs might miss out.

"In the short term the children will be physically and mentally compromised and in the long-term I think they will be really compromised because they will have successive years of much less therapy."

Education Minister Anne Tolley wants the therapists' budget for a $51 million funding pool that will enable a further 1100 children with special needs to qualify for a grant referred to as ORRS (Ongoing and Reviewable Resourcing Schemes).

She said this would make special-needs funding more equitable as only some schools received the additional therapist funding, which Ms Tolley said should have stopped when ORRS was introduced in 2001.

The minister said she had to find the extra $51 million to extend ORRS funding. It was not an easy decision to "take that support away from children that need every little bit of support they can get".

Labour's spokeswoman on disability issues, Lynne Pillay, said: "You're talking $2.5 million. It is nothing in terms of the $35 million that's been boosted into private schools. It's taking from the least privileged and giving it to the most privileged."