The school has been in conflict with the all-boy Sandbach school across the road, which has blocked the move because it is worried its pupils will be poached. Sandbach high is expecting a second rejection from the local admissions forum any day now, but in recently applying for foundation status, it could win the autonomy to decide on its sixth-form admissions without external interference.
The mission, according to head teacher John Leigh, is to stop a migration of around 20 per cent of his girls, and boys from Sandbach, to nearby co-ed sixth-form colleges.
In order to keep those students, both schools have been trying to collaborate on a single sixth form for the past 15 years, but without reaching an agreement.
Some parents believe the resulting competition for students will harm both sixth forms, as they try to outdo each other.
"We have tried for a single sixth form and failed," said Mr Leigh, who believes pupils benefit from mixed A-level classes.
"I am happy for girls to leave and go to the boys' school if it is better for them, and for boys who want to leave Sandbach and come here. There is nothing wrong with a little competition.
"Pupils go to the sixth-form colleges from both schools and many refer to the co-ed aspect as a reason for leaving," said Mr Leigh. "We want to stop that migration."
Opponents believe Mr Leigh has only applied for foundation status to push through what they believe are widely opposed changes intended to steal pupils and the funding that comes with them at the expense of the boys'
John Cargill, a parent governor at Sandbach, said: "It will be damaging for both schools if it goes ahead."