A tiny prick made a drop of blood on Nkosi Minenhle's finger, as the 15-year-old underwent an HIV test in a mobile clinic set up on her high school grounds.
A few minutes later a single black bar appeared on the test kit: She was not infected.
"I feel happy, I am able to tell my mum," she said, with a small, nervous smile. "And I know how to behave to remain negative."
The test was conducted by Mpilonhle, a charity that has since 2007 brought teachers, social workers and nurses to schools in Mtubatuba.
Only a handful of organisations organise HIV tests in schools in South Africa, the country hardest-hit by the virus that infects 5.7 of the 48 million population. Nine percent of people younger than 20 have HIV.
Hoping to improve treatment for youths, the government in February decided to expand testing, proposing that all students older than 12 get checked.
Children's advocates immediately called for caution, fearing that students would feel forced to take the test, even if they weren't emotionally prepared for a positive result.
"We underestimate adolescents' knowledge. They are far more knowledgeable than we give them credit for," said American pediatrician Michael Bennish, who founded Mpilonhle, which means "Good health" in Zulu.
"All adolescents, by definition, have elements of maturity and immaturity. With proper support and good counselling which is friendly to them, they can make a mature decision."
About one quarter of the students offered testing by Mpilonhle declined to take it.
At Madwaleni high school, one 17-year-old girl turned down the test. Her face drawn and downcast, she said she had sex with an older man and fears the possible result.
"I am afraid," she said. "Once I know that I am positive, my school work will be afected."
Mpilonhle's top educator Gugu Zulu said such stories highlight the need for testing in schools.
"You can't pretend that these teenagers are not sexually active, when they are. They are no longer innocent angels," she said.
Half of South Africans lose their virginity at age 16, and girls sometimes have relations with older men in exchange for small gifts.
"Because most parents are unemployed, to get things, the kids will go out with sugar daddies to get money from them," said Andile Zulu, a social worker for Mpilonhle.
That leaves girls more exposed to the virus. Six percent of 12th-grade girls tested by the group were positive, compared to less than three of boys in the same grade.
Despite the health risks, talking about sex remains difficult within families.
"Some mothers, if they are asked about sex, they can punish you or not answer you," said Victoria Makhunga, 18. "They will say, you are too young to ask about this."
Bennish says that's why it's important to provide another outlet for questions on sex, in individual conversations or in group discussions.
"It is complex to do (testing) at schools, but from our experience, it works best when it is part of a comprehensive programme," he said.
The challenge for South Africa is that the programme Bennish promotes costs 50 dollars per student, and would need to target six million students, in a nation already struggling to meet its youths' educational needs.
"We always have to make sure that it doesn't interrupt the other missions of the school in terms of academic activities," he said. "But, point emphasized, academic activities are no good for a dead person."