Two full schools in Brighton are being told to squeeze in almost a couple of dozen more children between them.
The 22 pupils are among 115 children who were “directed” to a secondary school, according to admissions statistics published last week.
The other 93 had either applied only to go to schools outside their catchment area or their forms had not been filled in properly.
Brighton and Hove City Council, which runs the admissions process, said that experience suggested that places would become available between offer letters being sent and September.
Some families move, others opt for another school, perhaps an independent school.
The council was confident that Dorothy Stringer and Varndean could take the extra 22 pupils without breaching their capacity.
Pinaki Ghoshal, executive director of children’s services at Brighton and Hove City Council, said: “In this year’s school admissions round 22 pupils could not be allocated places within the Varndean and Dorothy Stringer catchment in which they lived.
“It is the first year in which this problem has arisen and we have been in discussion with both schools regarding possible options.
“I am concerned that both schools are genuinely full with published admission numbers that have increased significantly over the years and concerns expressed by Ofsted in its report about Dorothy Stringer about the building.
“I agree with the governing bodies and head teachers of the two schools that additional pupils above published admission numbers may have an adverse effect on the performance of the school overall.”
Mr Ghoshal said that he could not change the waiting list criteria retrospectively. And he did not want to impose upon the schools more pupils than was in the interests of those schools as a whole.
He said that the 22 pupils would be randomly allocated one of the two schools and added: “Parents will of course still have a right of appeal as with any existing offer.”
The closing date for appeals is Monday 31 March.
Parents and carers are due to hear which school the 22 pupils will go to after midday today (Tuesday 11 March).
Mr Ghoshal said: “I believe this will remove uncertainty and allow secondary schools to work with the relevant primary schools to provide a better transition into secondary school, while at the same time protecting Varndean and Dorothy Stringer from numbers which are not in the interests of the whole school community.”
He added that the situation had reinforced the need to keep the catchments and admissions process under review as the population changed.