Delegates at the National Union of Teachers (NUT) annual conference in Harrogate have passed a resolution calling for all schools to include a positive view of same-sex relationships as part of their sex education policies.
The conference was told that gains have been made in society on Lesbian, Gay, Bisexual and Transsexual (LGBT) rights, but that homophobia, biphobia and transphobia are still prevalent in schools.
An NUT survey of LGBT teachers also found only 10% felt confident in disclosing their sexuality or gender to students and only 18% felt that all staff in their school consistently challenged discrimination against the gay community.
The resolution said: "Conference demands that a future government must tackle the embedded homophobia, biphobia and transphobia that exists in schools and create a positive climate of understanding about sexuality and gender fit for the 21st century.
"This must include a commitment to make it easier to discuss ideas about sexuality and gender so that students and teachers are more confident to identify as LGBT and work in schools without fear of prejudice."
The motion set out a series of measures for the union to take, including calling on the government to "make it compulsory that all schools' sex education policies include a positive portrayal of same-sex relationships."
National Union of Teachers (NUT) members are expected to issue a call for a ballot on national walkouts over funding cut.
Teachers have claimed that children are turning up to school sick because their parents cannot afford to take time off to care for them.