An exam body has reported a record demand for transfer tests in Northern Ireland this year.
The Association of Quality Education (AQE) is one of two bodies in Northern Ireland who arrange post-primary exams for entry to grammar schools. Stephen Connolly, AQE's joint chief executive, said 8,700 registrations had been received this year which he called an "unprecedentedly high figure".
The 34 member schools provide 8,100 places for primary seven pupils to sit the exam.
The overspill of 600 has meant some parents received letters to say their children will sit the exam at South Eastern Regional College (SERC) in Lisburn.
The arrangements have caused anger with some parents, according to Stephen Elliott from the Parental Alliance for Choice in Education (Pace).
"Imagine if you're a 10-year-old in the greater Lisburn area; you get a letter from AQE to say you're assigned to Lisburn tech to take your tests," he said.
"Not your primary school or the grammar school you hope to attend.
"Parents are absolutely not requesting this. I was called by a mother and grandmother who were very upset about it."
He continued: "When you then have something as vital as the AQE tests which cost schools nothing, AQE are arbitrarily deciding where youngsters, who are already anxious about the future, have to sit the exam."
Mr Elliott said he believed part of the problem was difficulty in securing teaching staff to supervise exams held on Saturdays.
Mr Connolly said he could well understand why some parents could have been "disconcerted" by the arrangements.
"It would be very difficult to cope with the numbers even if the applications were evenly distributed across all schools," he said, "but, almost inevitably, the over-subscription is to be found in what I shall call rather loosely the greater Belfast area, in particular Lisburn."
Mr Connolly said the high popularity of the Lisburn schools meant the available spaces for assessments filled up quickly.
"It follows that they are not able to take candidates whose registrations are submitted late in the registration period," he said.
"We always try to accommodate the parents' choices, which are ranked in order of preference from one to four, but the later in the registration period a registration is submitted, the more difficult it becomes to do that.
"We try to make that clear on the registration form.
"We then look at member schools who still have spaces left and would make our best endeavours to place a child in the nearest available."
Last year, overspill arrangements meant some children had to travel 20 miles away to sit the tests in a different school.
"We were faced with a small number of parents who did not feel able to accept a place in a school so far away, although the majority did so without protest," Mr Connolly said.
"The situation was resolved when, making extraordinary efforts, schools in the required proximity released some additional spaces."
Mr Connolly said the arrangements for an overflow centre with SERC were made to minimise inconvenience in the Lisburn area.
Mr Connolly concluded: "In other words, while our wish is always to place any child in the centre of his or her choice, the scale of the registration has prevented us from doing that.
"Our member schools do the very best they can, but their resources in rooms and staffing are not limitless and AQE has to achieve the best solution it can in those circumstances."