Secondary schools in Bristol will have to find places for 200 extra children next year because a new academy will not be ready in time.
Parents have called the delay “unacceptable”.
Oasis Academy Temple Quarter gained planning approval from the city council in August, with temporary accommodation expected to be available from September 2021.
But Bristol City Council confirmed no places will be available in time.
This means existing schools will be expected to take on the additional demand.
Jenny Grinsted, whose son was a prospective student, said: “It’s completely unacceptable that our children’s life chances will be affected forever by their failure to address this issue.
“Existing schools being required to take many more children than they were designed to now potentially threatens the quality of education for every single child in east Bristol.”
Mrs Grinsted added the money set aside for temporary accommodation should now be given to east Bristol schools instead.
The school has been delayed due to concerns about flooding, raised by the Environment Agency, because it will be alongside the city's Feeder Canal. It means the government must consider whether to intervene in the decision to grant planning consent.
A government “call in” would entail a public inquiry, the results of which would not be known for at least six months.
The council has also been unable to find any suitable sites for temporary accommodation that the Department for Education (DfE) is satisfied would be ready by September 2021.
A Bristol City Council spokesperson said: “We are working urgently to secure additional temporary accommodation capacity in existing schools to accommodate the need.
“We are also working with both the DfE and school trusts to ensure sufficient Year 7 places in 2021, with existing schools being required to take additional pupils to meet the demand.’’