Children with special educational needs will receive just three quarters of the additional teaching resources they are entitled to from this September.
It is the result of cumulative cuts that have taken place over the past two years in addition to further cuts announced today.
Announcing the allocation of resource teaching hours for schools for next year, the National Council for Special Education said the number of students in need of supports would increase by more than 10%.
It said with over 4,000 extra students needing support, the basis for allocating hours has been adjusted in line with resources, but there is a cap on the number of resource teachers allowed in the system.
Primary teachers' union the INTO has strongly criticised the resulting reduction in the allocation to individual students.
The union has accused the Department of Education and the council of attempting to hide the extent of the cutbacks from parents.
A spokesperson for the Irish Primary Principals' Network, Enda McGorman, has said there is a sense of absolute bewilderment in primary schools.
Mr McGorman said they are absolutely stunned at the level of the cut.
Speaking on RTÉ's News at One, Mr McGorman said it was a 25% cut relative to last year and even more so in his school in Dublin.
He said the Department of Education had made a clear decision that the people who would bear the cuts are the children on the ground.
NCSE Chief Executive Teresa Griffin said the "adjustments" to resource teaching would be a challenge.
However, she said unlike other areas of the public sector, schools were being asked to do more with the same allocation of resources, rather than more with less resources.
Ms Griffin said the number of resource teaching posts and special needs assistant posts had not been cut, and was the same as last year and in previous years.
However, the number of children eligible to receive resource teaching support this year had increased, and that had meant an adjustment in the allocation to individual schools in line with the number of posts available.
Speaking on the same programme, she said: “We are calling on schools to use small groups, to use team teaching, to look at how to use additional teaching support that is being made available.”