Almost a thousand people have signed a petition campaigning for the age range at Eskdale School to be altered.
Parents are appealing to education bosses at North Yorkshire County Council to implement the changes which would put an end to the controversial transition stage at the end of year nine.
They want the school to become an 11-16 establishment, meaning that pupils can sit their GCSEs at the school rather than have to move to Whitby Community College at the age of 14.
It comes after an application to turn Eskdale into an Academy, taking it out of local authority control, was turned down.
It also coincides with the merger of Caedmon School, where pupils also move after year nine, and Whitby Community College – which was given the final go-ahead this week.
A group of parents decided to get involved in a bid to back Eskdale as a school and help secure its future, but were surprised by how quickly support for their plight grew.
Helen Brown, whose daughter Charlotte attends Eskdale, is one of the organisers along with Jo Collier.
She said: “We only started it about three weeks ago.
“A handful of us got together and it got bigger and bigger. Lots of other people heard about it and wanted to know where they could get hold of a petition.”
Petitions were placed in local shops and doctors surgeries. Signed copies have since been sent to Pete Dwyer, director of children’s services, Coun Arthur Barker who has special responsibility for schools, Richard Flinton the chief executive and local MP, Robert Goodwill.
The changes taking place at the town’s three senior schools are the biggest to hit education in Whitby for decades.
Campaigners say the shake-up is needed to give parents choice and also because the education system in town is out-dated compared to the rest of the country.
Jon Brown said: “I am not from Whitby but when I saw the secondary education set up I thought it was ridiculous. It just goes back 40 years to the old grammar school system.
“It is recognised by everybody in education that the transition period is not good.
“It is right at the beginning of the vital stages of pupils’ GCSEs.
“They are getting used to new teachers, new schools and new routines.
“It is not about being against the merger but we would imagine Eskdale would run independently of it.”