Stonewall Cymru education officer Luke Young says he is surprised to learn of large numbers of schools in south-east Wales with no recorded cases of homophobic bullying.
South Wales East AM Lindsay Whittle has urged schools to identify homophobic bullying as a separate issue.
Recorded cases of homophobic bullying in schools could be 'the tip of the iceberg', an Assembly Member has warned.
South Wales East AM Lindsay Whittle submitted a freedom of information request to schools in his region asking how many anti-gay incidents headteachers had to deal with in a five-year period.
Seventy-one incidents emerged in total - but some schools had no recorded cases at all.
Research by lesbian, gay and bisexual charity Stonewall has shown that over half of all lesbian, gay and bisexual pupils experience homophobic bullying.
Mr Whittle said: "The fact that many schools have no recorded incidents of homophobic bullying over the past five years makes me think whether or not all schools identify homophobic bullying separately from bullying accusations generally.
"I believe these figures are probably the tip of the iceberg and I urge all schools to treat the issue of homophobic bullying with the seriousness it deserves, record incidents and take the appropriate action when necessary."