Parents were encouraged to be ‘informed and open-minded’ and consider choosing secondary schools outside of Adur at a meeting on Thursday.
Rising pupil numbers in the district meant that children in Shoreham could no longer be guaranteed a place at Shoreham Academy, parents were told.
Alastair Reid from parent campaign group Future Adur Schools Team (FAST), which organised the event, said the population drift from Brighton and housing developments planned meant it might be necessary for 800 to 1100 new secondary school places in Adur in the next decade.
“A school’s worth of kids is coming down the line,” he said.
Representatives from the Sir Woodard Academy in Lancing and Portslade Aldridge Community Academy attended the event to reassure parents that they had capacity to accept pupils from Shoreham – at least for now.
Both schools said they would work with parents to arrange transport for pupils from Shoreham if required.
But Mr Reid said a new secondary school in the district was probably needed and could not wait until all existing schools were at capacity.
“That doesn’t quite work, you can’t just magic up a new school,” he said.
“There needs to be some overlap. That’s why you have to think long term.”
David Etherton, head teacher at St Nicolas and St Mary CE Primary School which is planning to open a new primary school, said creating a new school took a minimum of about four years.
Jim Coupe, principal of Shoreham Academy, said: “I share the long term concern about the school places.
“In reality, Shoreham Academy, PACA and SRWA will be full and oversubscribed.
“There will be too many young people for the school places available.
“What FAST is doing is really relevant.”
After the meeting, Mr Reid said: “It was a really good turnout, there was over a hundred people, the hall was packed. We’ve had lots of positive responses.”
West Sussex County Council, which did not attend the meeting, will address the issue at the next Adur County Local Committee on Thursday, June 21 at 7pm (venue to be confirmed).