Pupils interviewed for "Listening to the boys", a study on attitudes to sex education, overwhelmingly believed that maths teachers "can't cope" and "are generally dreadful".
In contrast, English and history teachers were experienced in active teaching methods, such as role-play and discussion, seen as appropriate for sex-education classes.
More than 300 boys, from both state and independent schools, were interviewed for the study in this month's international journal, "Sex Education".
Gillian Hilton, principal lecturer in education at Middlesex University, and author of the paper, said: "Boys are desperate to learn. But teachers are often completely untrained, and cannot use the right methods."
Bill Richardson, chair of the Maths Association, defended his colleagues' abilities. He said: "Yes, maths teachers would need a different style of teaching. But with training, they are just as capable as others."