Schoolgirls from Mphaphuli Secondary in Limpopo are so afraid of being propositioned by teachers that they go in pairs when they visit the staffroom.
"If the teacher proposes and you deny him ... he will make you fail," one said.
The pupils at the school in rural Thohoyandou describe the teachers as "blessers" who sleep with girls in exchange for buying them lunch and awarding them top marks.
Three teachers had relationships with matric pupils last year, while another teacher was in a continuing relationship with a Grade 11 pupil, they said.
While the school principal and governing body declined to comment this week, the claims against the school are not unique.
A survey by an NGO at six schools in the region found that 129 pupils had been "propositioned" by teachers last year. The sex-for-marks phenomenon was so common that the NGO, the Thohoyandou Victim Empowerment Programme, labelled it "sexually transmitted marks".
At one of the schools, eight in 10 pupils said they did not believe they had the power to say no when a teacher demanded sex.
When the Sunday Times visited the area this week, a matric pupil at another school told how a teacher had mocked her openly in class after she rejected his sexual advances. "He then asked me for my telephone number and I didn't give it to him but he ended up getting it from my friend."He said he would urgently investigate whether his teachers were having inappropriate relationships with pupils. "I will make the results of the survey available to parents. If I did not get this [survey], I wouldn't have known. Worse can happen if I don't act. Schools should be safe places for learners."
Fiona Nicholson, programme director of the NGO, said: "Even if girls are flirting and trying to seduce educators, obviously the educators are the adults so they have to resist that.
"Too many girls are still having their self-esteem bred out of them from birth in patriarchal areas like ours.
"They are not averse to using their bodies as a means of getting good marks because they have been raised to believe they're nothing and they are just there to please men and to look after men."
But Nicholson said the NGO had received encouraging responses from school governing bodies.
South African Council for Educators spokesman Themba Ndhlovu said the problem of teachers propositioning pupils was rife across South Africa...