The Lord Of The Rings star spoke about his campaign in Attitude magazine, where he called on other homosexual men to go back to their former schools to discuss homophobia.
Sir Ian, 69, said: "It is essential to talk to 12 and 13-year-olds because they absorb what's thrown at them, whether it be homophobia or tolerance - and we have to make sure it's positive stuff.
"But there are 30,000 schools. I think this campaign is right - any openly gay person should consider whether they have a duty of contacting their old school and saying 'You may not know, but I am gay and I was when I was at school and what is your policy with regard to homophobic bullying?'."
The actor said he was invited to one school by the headmaster as two pupils had just come out. The head believed they were the only two homosexual pupils at the school and did not know how many members of his staff were gay.
"He had no idea. And this was a concerned man. There is a need to make it clear that there are gay kids in school," he added.
Sir Ian publicly came out as gay on BBC Radio 4 in 1988 while discussing Margaret Thatcher's Section 28 legislation which would make public promotion of homosexuality a crime.