Psychologists providing assessment of school children with special needs are said to be unable to take on any new students until funding has been made available by the Department of Education.
At present schools not included in the National Educational Psychological Service (NEPS) are permitted to engage the services of external psychologists, with the cost being reimbursed to them by the Department.
This is done on a quota basis, with schools allowed to have one student in every 100 assessed.
However, the budget for this service expired at the end of 2003. A spokesman for the Department confirmed that, while funding was available, the particulars of how it would be allocated were being worked out.
This means that schools which are outside the NEPS programme do not currently have the facility to have their students assessed, according to Mr Seán Cottrell, of the Irish Primary Principals' Network.
Describing assessment as the "foundation-stone" for students with special needs, he said that even those schools which are covered by NEPS are subject to a "wafer-thin" service.
However, delays in organising the provision of outside services were hitting the most vulnerable children.
"A fairly good proportion of schools are not within NEPS," he said. "This is an extremely disappointing breakdown in a system which is in itself imperfect.
"The quality of service where it is being provided is very good, but the problem is that the case-load is simply enormous. We would like to see it organised on a needs basis rather than a quota basis."