The planned reorganisation of Cardiff's largest school has been criticised by governors, who say it will reduce parental choice and education quality.
There are 8,000 empty school places in Cardiff
There are proposals to reduce Whitchurch High School to one site as part of a city-wide education shake-up to tackle 8,000 empty school places.
It would mean pupil numbers would be cut, but a new primary school could be built on the land not being used.
But Cardiff Council said the plan would mean enhanced facilities for pupils.
In a letter to the council committee overseeing the schools shake-up, Whitchurch High chair of governors Joyce Crandon criticised the proposal.
The council said the school, which has more than 2,350 pupils, could be reduced because about 400 pupils attend from outside the catchment area.
But the school said of that number, 200 were sixth-formers.
"All sixth forms in Cardiff are open access and pupils attend the school or college where there are courses on offer that interest them," Ms Crandon said in the letter.
"Many of our out-of-catchment sixth-formers previously attended 11-to-16 schools."
She said governors felt the proposal did not meet with Welsh Assembly Government criteria for school rationalisation.
"It does not offer the same quality and diversity of education, it curtails parental choice, it does not offer best value and it would not reduce the current level of surplus places within the authority," she added.
Cllr Brian Griffiths, a governor at Whitchurch, said there was opposition to the school moving to its lower school site off Manor Way.
"It would be cramped even it was down to nine-form entry, but it would also mean a loss of a lot of the playing fields, cricket pitch and the new sports building."
He said a meeting had now been arranged for September to bring together governors and heads of the schools affected, as well as the council leaders.
Bill Kelloway, the council's executive member for education, said he was "surprised and disappointed".
He said more consultation would be carried out on the plans, which include the closure of two primary schools and the building of a new one to replace them.
"Difficult choices have to be made when it comes to the emotive subject of reorganising schools but I have been extremely disappointed by the negative reaction among some parts of the community," he said.
"Facilities for all children would be enhanced and modernised, not reduced.
"Parents would be guaranteed a place for their child at the local school, whether that be in the English-medium or Welsh-medium sector, thereby improving parental choice, not curtailing it, which can only be a positive thing.
"I find it difficult to believe that anyone who truly says they are concerned with education can be so unwilling to consider options which could have a massive benefit to all children living in the Whitchurch area."