According to The Independent and Union NASUWT in the UK, about twenty-five percent of non-straight teachers are closeted to their students and coworkers.
As one of the leading homophobic arguments against LGBT-equality is that same-sex practices are gateway behaviors, leading to incest, bestiality, and pedophilia (which they're not!), this should be an obvious discovery in an educational setting.
In the US, we're no stranger to teacher-student sexual relations, but the high and distant majority of these cases are heterosexual, a female teacher with a male student or a male teacher with a female student. If anything, their argument could be reversed, that opposite-sex practices are gateway behaviors, but we're more interested in equality all around than turning the tables and promoting reverse-discrimination.
The Independent goes on to list more released statistics, but they all tell the same story.