All new and existing teachers will be trained in tackling homophobic bullying under Labour plans to eradicate anti-gay prejudice from schools.

Unveiling measures to support the estimated 215,000 lesbian, gay and bisexual pupils in British schools, the shadow education secretary, Tristram Hunt, said schools had a duty to show “a zero-tolerance approach” to homophobia in the classroom and playground.

He said: “The use of homophobic language and other forms of homophobic bullying is damaging the life chances of so many young people … There is no place for it in our society – and never should it be ignored in our schools.”

Under the plan, age-appropriate sex and relationships education will become compulsory in all schools, including in academies and free schools, which are currently exempt.

Hunt said Labour would promote mental health services for young people who had been victims of homophobia and said a “toolkit” of national best practice would be made available to all schools.

According to figures published on Tuesday by Stonewall, 52,000 gay, lesbian and bisexual pupils – about a quarter of the estimated total – will miss school because of homophobic bullying, while the schoolwork of 70,000 will suffer. It estimates that 37,000 will change their future plans because of homophobia.

The charity, which works with 12,000 schools across the country, welcomed Hunt’s announcement, saying homophobic bullying and language were endemic in schools.

Hunt says section 28 still cast a shadow over the education system. Photograph: Anthony Devlin/PA

“We have seen progress under this and the previous government but more still needs to be done,” said Hannah Kibirige, Stonewall’s senior education officer.

“We welcome this commitment and will be calling on future governments to ensure that every teacher is equipped to tackle homophobic bullying and that every young person can reach their full potential.”

Hunt said the legacy of the “pernicious” section 28 legislation – which was introduced under Margaret Thatcher in 1988 and banned the “promotion” of homosexuality in schools – still cast a shadow over the education system.

“That is why repealing section 28 alone [which happened in 2003] is not enough. We need new training for new and longstanding teachers and others in the school workforce … And we need to act urgently to prevent the plight of homophobic bullying that is damaging the lives and life chances of thousands of pupils.”

Linda James, chief executive of the anti-bullying charity Bullies Out, said it was vital to address homophobic bullying and language in schools.

“Although training our teachers will help – and they should be trained on dealing with all aspects of bullying – more needs to be done from a higher level. We need increased support and increased mental health services for young people affected by this.

“Although a toolkit will be an excellent resource, schools must show a zero tolerance to bullying and unless they do, the toolkit will have no benefit whatsoever.”

Teaching about puberty is often left too late Lucy Emmerson, national coordinator of the Sex Education Forum

Lucy Emmerson, national coordinator of the Sex Education Forum, said she welcomed the commitment to make sex and relationship status compulsory in all schools and end the “shabby status” of the subject.

“When teachers are properly trained in the subject they can explore topics such as family diversity with the youngest children in a way that includes everyone and builds the foundation for a school free from homophobia, biphobia and transphobia.

“Currently, there is no requirement for primary schools to teach about relationships and teaching about puberty is often left too late.

“The result is that many young people leave school having learned nothing about consent and with fragments of information about their bodies and sexual health.”

Mary Bousted, general secretary of the Association of Teachers and Lecturers, said she was delighted at the proposals to provide training for student and current teachers and called for this to be extended to all education staff.

“The plan also echoes our calls for young people to receive high-quality sex and relationships education in an age-appropriate manner.

“We hope this will be an effective step towards ensuring that all lesbian, gay, bisexual and trans young people are able to reach their full potential without the fear of bullying or discrimination.”

Nicky Morgan, the education secretary, said: “[The government] made tackling homophobic bullying a priority in the coalition agreement and since then we’ve invested in projects to train more teachers on tackling homophobia in the classroom and set out clear guidance on the importance of tackling all types of bullying, including homophobic bullying.

“We’re pleased that teachers are now reporting lower rates of homophobic bullying compared to five years ago and greater confidence in tackling this bullying.

“Of course there is no room for complacency, which is why we recently announced a £2m fund to support projects to combat this bullying in our schools and take us a step closer towards our goal of eradicating this bullying from our classrooms.”