President Cyril Ramaphosa has slammed sexual relationships teachers had with pupils as "abhorrent behaviour", asking for it to be stopped.
"Bagaetso (our people), we know that it is happening," said Ramaphosa.
He was speaking at the SA Democratic Teachers Union's 9 th national congress in Nasrec on Wednesday.
Ramaphosa said there were too many reports of sexual relationships between teachers and pupils and challenged denialism about the behaviour among some in the teaching fraternity.
"As educators, your job is that of a parent of the children who come to your school. You are not supposed to be the lovers of your children who come to your school," said Ramaphosa.
The president urged Sadtu to be at the forefront of fighting the scourge.
"These crimes must be fully prosecuted, and the perpetrators must be subjected to the full might of the law," said Ramaphosa.
He said teachers should not remain silent when they see that their pupils are in distress.
"Educators are often the best placed to notice where learners are victims or at risk and we urge you to speak out. This culture of silence empowers and enables perpetrators," he said.
He added that there was a need to shift society's mindset so that patriarchy can be rejected, and to remove the harm gender stereotypes cause boys and girls.
"Teachers who have consistent contact with young people are vital to changing mindsets and empowering young people to deal with harmful social relations," he said.
While calling for greater vigilance from teachers, Ramaphosa acknowledged that they were "overburdened and under-resourced".
He said it was the government's duty to resolve this and ensure teachers are well-equipped and supported to play their role in society.
A dark cloud hanging over South Africa
The president, who discussed the recent spate of xenophobic attacks and increasing cases of femicide, said it was like a dark cloud hanging over the country and that collective effort was needed to clear it.
He repeated a message he carried over the past few weeks, that South Africans were not xenophobic.
Ramaphosa also said the news of violence in the country, was " splashed" across the globe and led the African Union to meet over the issue.
In addition, he sent an envoy to numerous African countries to explain what took place in the country and to share plans on how his government was addressing the matter.
Ramaphosa said his government's responsibility was to South Africans, ensuring they get jobs and services.
However, he said while foreigners live among them, there should be tolerance.
"We've also said that those who have come to our country to live, must obey the laws of South Africa as they live here," he said.