Criticism is being expressed over plans by a Kent boys' grammar to become a "super-selective" school.
Primary school pupils in Kent can still sit the 11 Plus
Maidstone Grammar gives priority to brothers of pupils and those who live nearby, but now wants to accept only those who pass highest in the 11 Plus.
"I think it is going to create considerable unhappiness, uncertainty and distress," said independent educational adviser Peter Read.
Head teacher Neil Turrell said the school wanted to control its destiny.
The grammar, which was founded in 1549, became a foundation school in September which gave it the power to set its own admissions criteria.
If it takes pupils based purely on their marks in the 11 Plus, called the Kent Test, parents in Maidstone fear their children could be excluded in favour of entrants from neighbouring towns or even adjoining counties.
Carpenter Adrian Pearson has two sons at the school but fears his youngest may not get a place.
"I can understand why MGS would adopt this policy but it does seem a little cold-hearted - even cruel," he said.
Mr Turrell said the school was consistently over-subscribed.
"We did not set out to become a super-selective school," he said.
"The governors have been concerned over the past 10 to 15 years that the boundaries of the catchment from which we take students is effectively decreasing.
"I have a significant number of applicants from Borough Green, Cranbrook and Staplehurst who are denied access to the school because of where they live."
He said the school also had "issues" with the independent appeals panel which adjudicates when parents are not satisfied with the schools their children have been allocated.
Details of the planned changes are being sent to parents and primary schools in the area.
The governors will consider the responses before making a decision in November.