The girl was found hanging in the storeroom of her house and a newspaper with matric results was lying on the floor, Captain Fezile Malesa said. She was a pupil at Thomas Mofolo High School.
"There was no suicide note, but we believe she committed suicide after finding out that she failed her matric.
"A newspaper was found in the room and on her we found a cellphone which had a message telling her she did not make it."
The 18-year-old girl lived with her elder sister and cousin in the house in Emndeni.
Police opened an inquest docket.
Minister for Women, Children and Persons with Disabilities Noluthando Mayende-Sibiya expressed shock at the incident and conveyed her condolences to the family.
She advised parents to support unsuccessful pupils and urged them to try again.
"Parents and families must support learners who have been unsuccessful in their matric examination. It is in difficult moments like these that our children need us most as parents.
"Let us help learners to understand that poor results do not mean the end of the world. There is always an opportunity to try again and improve on your educational outcomes," Mayende-Sibiya said.
Just R20 for the first month. Support independent journalism by subscribing to our digital news package. 