The six appeals, to the school's governors, were conducted separately at the end of last week. It is understood that the four other appeals have also been denied.
On 7 March, about 200 of the East Sussex school's 1,700 pupils left the premises with the intention of marching into town to demonstrate against the then-imminent war with Iraq.
Teachers rounded up most of the pupils and persuaded them to return to school. All protesters were punished with detention, but six GCSE students were handed fixed-term exclusions, which effectively means they will only be allowed back to school to take their final exams in May and June.
Neil Hunter, headmaster at Blatchington Mill, said: "Six of the protesters were persistent troublemakers, who had all been warned in the past about their attitude and behaviour. They were told that if anything else happened, they would be considered for exclusion."
But one of the pupils, 15-year-old Sarah McMurray, said: "It's not the teachers' place to tell me how to protest. Adults seem to think they're the only ones who care. We wanted to show that young people also care about what's going on in Iraq.
"It's shocked me that I've had such a bad response from the teachers and the school. They always tell us to speak freely, but when it happens, they criticise it."
The Department for Education and Skills has said that young people must not walk out of lessons and lectures to protest.
The DfES told YPN: "Pupils have the right to protest outside school hours.
However, as education and skills secretary Charles Clarke has made clear, we do expect pupils to be in school during school hours.
"Unauthorised absence is truancy and head teachers will take the appropriate action to deal with it."
