James Hudson, 18, and his mother, Nora, are calling for the head of the 447-year-old Leeds Grammar School to resign after he imposed a suspension of one week on the other pupil involved.
James, who says he has been openly gay for two years, claims he was head- butted in the sixth-form centre of the pounds 5,800-a-year school before Easter. He said yesterday the lenient punishment given to his alleged attacker of a few days' suspension suggested the school was biased against him. The school insisted that the matter was "settled".
James, who is due to take A-levels in English, French, economics and general studies this summer, and who hopes to study history of art at university, said that he could not return to school while the other pupil was allowed to attendlessons.
He said: "I want him to be expelled - that's not unreasonable. I have done nothing wrong." Earlier this year, James organised a petition demanding an apology from the school's headteacher, Bryan Collins, after he told an assembly that gay sex was "abhorrent".
"I want the headmaster to resign," James said. "And I want Leeds Grammar School to accept that they are negligent and [for it] to have a change of policy to say that bullying - for whatever reason - is not tolerated.
"I am sad that after I have spent eight years at a school, and they have given me so much, that they have turned their back on me."
The matter flared up earlier this month when James handed teachers a letter from his mother addressed to the head, complaining about his treatment. In it Mrs Hudson said: "Leeds Grammar School has a contractual obligation to provide my son with an education and to prepare him for his A-levels in a safe, caring environment, free from prejudice and hate. You have failed, through your negligence, to meet these needs. You leave us with no alternative but to sue you."
In a statement, Mr Collins said: "During the week before the school's Easter holiday, there was a dispute between two members of the upper sixth form, arising, I understand, from an incident at a private party the previous weekend. The dispute, in the sixth-form centre during a break, resulted in one student injuring the other's nose.
"After investigating the matter, and following my reporting the matter to the governors, I suspended the assailant for the week following the school's Easter holiday. On his return he was given a final warning, banned from the sixth-form centre and put under restrictions to keep him away from the other student.
"The matter is now settled but I believe there has been a complaint to the police and that legal action may follow."
A police spokesman said an 18-year-old man was to appear before Leeds magistrates on 29 April, facing a charge of assault causing actual bodily harm.