The HSE has said that a letter should not have been sent to a Dublin family telling them they would have to wait more than five years for an appointment for their child.
Seven-year-old Lexi Forde has autism and is currently suffering from severe anxiety.
Her parents told RTÉ News she was struggling to attend school full-time because of anxiety and her school's lack of resources.
Sorcha O'Connor and Stephen Forde earlier said that they had been told it will be late 2026 before Lexi is seen by HSE school-age support services.
They said Lexi has been transformed from a happy outgoing little girl to one who now has great difficult leaving their home.
This evening, the HSE has told RTÉ News that Dublin South, Kildare and West Wicklow Community Healthcare should not have issued the letter and it will investigate why this communication was sent.
However, the HSE has not said when Lexi is likely to be offered supports.
Lexi's school, St Dominic's National School in Tallaght, has managed in recent weeks to coax her back and is managing her with a combination of one-on-one teacher support and limited integration back into her classroom.
However, the school said that its limited teacher and other resources mean that Lexi can only attend for a few hours each day.
It said it needed greater resources to allow it to support Lexi and other pupils with additional needs adequately.
Today, St Dominic's joined calls from a number of school patron bodies for an increase in the allocation of special education teacher hours next year for schools that are growing.
Last week, the school was informed that it would receive the same Special Education Teacher (SET) allocation next year as this year. Principal Séamus Vaughan said the school was devastated by the news.
Enrolment at St Dominic's is expanding every year, yet the school's teacher allocation for children with additional needs remains stuck at 2017 levels.
"Year on year we are expanding but our SET allocation is not catching up with that increase," Mr Vaughan told RTÉ News.
"I would dearly love to be able to do more for a child like Lexi, but we haven't got the staff to do it."
Lexi's parents have said they are heartbroken after a year of "crying and begging" for services for their child.
Last week, they received a letter from the HSE's School Age Service offering an initial appointment in November 2026. By then, Lexi will be in sixth class.
The letter stated: "This service currently has lengthy waiting lists for services.
"It is expected that Lexi will be seen for her first appointment, which will focus on the development of her Individual Family Service plan, in November 2026.
"Please note that this date will also be subject to change due to the effects of the current Covid-19 pandemic."
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Mr Vaughan said that giving an appointment for five years' time "cannot be called a service".
In 2017, St Dominic's was granted 168 hours of additional teacher time to help it support children with additional needs. Even then, the schools said, that provision was lower than what was required.
"We knew in 2017 that our allocation was wrong but we were told to wait until the new profile was done in 2019," Mr Vaughan said.
"In 2019, we were reprofiled and promised an increase of 50 hours of additional teaching time, but we were only granted 20% of this.
"In 2019, we had 332 pupils, now we have 384. Next year we will have more than 400, yet our Special Education Teacher allocation has not grown at all.
"Using the department's own criteria, the school calculates that it should be receiving 225 hours next year. That is more than one third more than its current allocation."
Mr Vaughan said Lexi was not the only pupil at St Dominic's who is suffering as a result.
"For some children we would like to be able to put in one-to-one teaching support. We would like to put in a daily intervention out of the classroom for a small period of time, but we can’t. We have to stretch the resources," he said.
Mr Vaughan said that staff can see the need and the impact when this intervention is not available.
"This year has been a really hard year for these children," he said.
"You see it in the classroom, in behaviour for instance, when they need to get a break when they are not able to cope."
Meanwhile, Lexi's parents said they have run out of doors to knock on. "Nobody is listening," Ms O'Connor said.
The HSE said this evening that it was currently rolling out a new programme to reorganise children's disability services.
It said the Progressing Disabilities Programme would change the way children and their families access and receive clinical disability services.
The HSE said it aims to provide a fairer pathway to clinical supports.
It said that this meant its current School Age support service, which is the service that Lexi was given the appointment for, will no longer exist from June 2021.