Homophobic bullying in schools is "endemic" and likely to rise with the impending growth in the number of faith schools, teachers warn.
The Catholic Church has already openly criticised the nationally agreed code of conduct for teachers that requires them to "proactively challenge discrimination" in school, teachers claim.
Delegates at the National Union of Teachers' conference in Harrogate added that the failure to tackle discrimination would be exacerbated by the setting up of new "free" schools – many run by religious groups – from September.
A motion overwhelmingly backed by delegates said: "Some religious schools believe they are above the law and can do anything that they believe is line with their religious beliefs."
Dave Brinson, of the union's executive, told the conference: "Discrimination, intolerance and bigotry have not gone away. They're still there and they still need to be challenged."
The motion, which also called on the union to conduct an investigation into discrimination in faith schools, was not "anti-faith schools", he said.
There were many that did a good job in combating prejudice – but there were others, "both faith-based and secular that don't challenge homophobia and discrimination".
Annette Pryce, from Buckinghamshire, said: "Homophobia is insidious for both staff and pupils – more so in faith schools."
Deborah Gwynn, from St Helens, Lancashire, revealed details of a survey which showed that 40 per cent of teachers had heard pupils use homophobic words on a daily basis. Less than half the teachers surveyed believed their schools had an effective policy for combating homophobia.
"We have to challenge the use of homophobic language by students no matter how innocent it might seem," she added. "People are using the word 'gay' and they are meaning boring, stupid or rubbish. How are you going to feel if people are using that word on a daily basis to mean something like that? We all have to challenge the use of the word 'gay' in this context."
A survey carried out by the School Health Unit for Stonewall, a lobby group on behalf of gays and lesbians, showed that almost two-thirds of gay pupils had suffered homophobic bullying at school. Of those who had been bullied, 41 per cent had been physically attacked and 17 per cent had received death threats. Half had missed schooling as a result.
Michael Dance, of Redbridge, spoke of his sorrow at seeing an ambulance coming to his school for a gay pupil who had suffered a panic attack as a result of bullying.
Leaders of the union added that teachers in faith schools could also suffer discrimination as a result of legislation that allowed heads to appoint staff on religious grounds. This could lead to favouring teachers of the particular faith of the school in promotions and appointments.
They warned that if a school did not tackle discrimination it could send a negative message to gay and lesbian pupils. "If a school has not got that commitment that our school is a safe place for all and does not challenge discrimination, the message gets through," said Mr Brinson.
"If you have a school that's not taking this problem seriously, [pupils] don't feel comfortable and feel they aren't going to be supported."
The motion warned that some schools were "unlawfully" using their faith status to avoid implementing equality policy.
It added that the conference was "alarmed by the Government's plans to push through academies and free schools" and called on the union to oppose "all groups who promote discrimination whether it is on religious grounds, e.g. evangelical Christian academies, or ideological grounds".
Of the first 11 "free" schools approved by the Education Secretary, Michael Gove, four were faith-based. Those applying to set up free schools included evangelical Christians who wanted to give their school a creationist ethos, and Muslims.
Dr Oonagh Stannard, the chief executive of the Catholic Board of Education, said it had been able to support the profession's code of conduct.
"Any form of bullying is completely unacceptable," she added. "Catholic schools have been noted for their low incidence of bullying."