Schools are not tackling homophobia or providing sexual health information, leaving young gay men more vulnerable to HIV, a campaign group says.
Homophobic bullying is common in schools, the Trust claims
The National Aids Trust, marking international day against homophobia, said homophobic bullying in schools was common and often unchallenged by staff.
It said sex and relationships education should be on the national curriculum.
The Department for Education said it was working to ensure schools responded adequately to homophobic bullying.
Trust chief executive Deborah Jack said schools must address the issue.
She said: "Increasing rates of HIV among gay men, high levels of homophobic bullying in schools and inadequate sex and relationships education are leaving young gay men more vulnerable than ever to HIV infection.
"We need schools to not only have policies of zero tolerance to homophobic language and behaviour but also to address sexual orientation and HIV in the curriculum. Homophobia should be as unacceptable in schools as racism."
The Trust claims many schools simply failed to address sexual orientation at all.
It said this, coupled with homophobic bullying, created an atmosphere of fear that was a disincentive for lesbian, gay or bisexual young people to get sexual health advice.
It added that HIV levels were higher now than they have ever been among gay men - 2,240 gay men were newly diagnosed with HIV in 2004 compared with 1,375 in 1998.
A spokesperson from the Department for Education and Skills said: "No child should suffer the misery of bullying, regardless of race, sex or anything else - every parent agrees with this.
"We are working to ensure that schools provide a clear focus on responding to homophobic bullying in anti-bullying training and materials for schools and teachers.
"We also support Lesbian, Gay, Bisexual, Transgender History month in schools to help young people understand the significant contribution made by all communities to the diversity and success of this country."
The shadow education secretary, David Willetts, praised the work of councils such as Barnet which he said had made it a priority to fight homophobia in schools and the workplace.
"It is equally right that all children receive the pastoral care and sex education appropriate to their needs," he said.