Primary-age boys use the words "gay" and "girl" as interchangeable insults to help to establish their own masculinity, she found.
Dr Renold will discuss her findings in Llandudno tomorrow at a conference organised by the gay rights group Stonewall Cymru to launch Education for All, a campaign against homophobic bullying in schools. The keynote speaker, education and lifelong learning minister Jane Davidson, is expected to focus on the need for effective anti-bullying policies in schools.
According to Stonewall, a survey of 300 secondary schools in England and Wales conducted in 2003 found that 82 per cent of teachers were aware of verbal incidents of homophobic bullying. While almost all schools had anti-bullying policies, only 6 per cent referred to homophobic bullying.
Dr Renold said young boys seldom know what gay means, "but know it's something wrong", and use homophobic abuse in two ways - "to prop up fragile heterosexuality and (as) a strategy of masculinity".
Her studies, based on two years of classroom research, found that teachers rarely saw the use of words such as "gay", "girl" and "sissy" as abusive, because it was often done through humour.
"Teachers themselves use these comments - they have to start with themselves," said Dr Renold, who also recognised that many teachers felt inadequately trained and unprepared to deal with homophobia.
She said progress had been made in tackling homophobic bullying, particularly since the repeal of Section 28, the law banning the promotion of homosexuality by local authorities. But research gaps remain: "We don't know how many schools have altered their bullying policy," she said.
A spokesman for the Welsh Assembly government said Jane Davidson would reiterate her call for schools to send her copies of their anti-bullying policies. The Government wants to assess how schools are tackling the issue and single out examples of best practice to be published later this year.
She is also expected to draw on the Government's sex and relationship education guidance from 2002 to discuss how schools should be developing lessons and working with parents.
Sylvia Jones, co-chair of Stonewall Cymru, acknowledged the Government's "unprecedented policy commitment to tackling bullying" and its support for lesbian, gay and bisexual young people.
But she added: "There remains a gap between policy and practice. We are convinced that homophobic bullying remains one of the most difficult forms of bullying for pupils, students, teachers and educationists to tackle."