More than 300 children with a statement of Special Educational Needs (SEN) are without a school place for September.
That includes 91 children waiting for a place in a special school and 202 seeking a place in a mainstream school.
The Education Authority (EA) said there had been a "significant rise" in demand for special school places.
It said it was "working hard" to ensure children with SEN had "an appropriate place" for 2022/23.
According to statistics from the Department of Education (DE), more than 22,000 school pupils in Northern Ireland have a statement of SEN.
A statement sets out a description of a child's needs and the help that is required to meet them in school.
About 6,650 of those pupils attended special schools in 2021/22 but the EA said that 668 more children needed a place in special schools by September 2022.
In response to questions from BBC News NI, the EA said that 91 of those 668 children still did not have a confirmed special school place - around 12% of those seeking a place.
Meanwhile, another 148 children are still seeking places in specialist learning support units in mainstream primary and post-primary schools.
Those are special classes or units which provide extra support to pupils with additional needs.
That means almost a quarter of children (22%) with statements of SEN who need a place in specialist provision in a mainstream school still do not have one.
'Mentally, emotionally and physically draining'
Tina Blackburne's 12-year-old daughter Leila has not been to school in five months and is still without a school place for September.
Leila has an official autism spectrum disorder (ASD) diagnosis and statement of education, ADHD and chronic anxiety.
"Since March of this year I can only describe as what we're going through as absolute hell," Ms Blackburne said.
"Leila went to mainstream school and was given a full-time classroom assistant but unfortunately it didn't work out for a number of reasons and I had to remove her from that school in March because she was traumatised from the experience she had been having.
"Last week I got a call to say 'sorry, the school you have chosen is full'".
'Desperately needs support'
Ms Blackburne, who lives in East Belfast, said Leila was offered a place in a school in Ballynahinch instead, something she finds "would be completely inappropriate" due to her diagnosis and make the situation even worse.
She has also said the Education Authority (EA) is failing children and parents who need help.
"I'm banging my head against a wall and dealing with a child that is really unwell and who desperately needs support," Ms Blackburne said.
"Imagine how you would feel if you were told you don't have a place in school...in a world you already feel different in.
"It is mentally, emotionally and physically draining.
"I don't feel the EA has been there to support me and a lot of other parents."
Raymond McFeeters, acting principal of Ardnashee School and College in Londonderry, said many of the children waiting for a special school place will have "heightened anxiety levels and difficulty with change and transition".
"It is much more important for those kids to know where they are going to, where they are going to be placed, and that people are able then to prepare them for that transition and change in their lives," he said.
Mr McFeeters said every parent has a right to know where their child is going to be educated
"It is really disappointing that we haven't been able to do more to facilitate that," he said.
'Increase in demand'
More than 60 other children with statements are also waiting for a place in a mainstream school to be confirmed, although they do not need to enter specialist units.
The EA said there had been a rise of around 35% in the number of pupils in special schools in just five years.
There were 5,407 pupils in special schools in 2017 but that will rise to over 7,320 pupils in September 2022.
The EA said that indicated "a significant increase in demand for special school places".
In 2021, a former high school in north Belfast became an additional special school to help meet demand.
The former Castle High School became a second campus for Harberton Special School.