Lisa Barrett, whose daughter attends Ysgol Dyffryn Aman school in the west Wales town of Ammanford, says her daughter texted her saying her secondary school was in lockdown.
She says there are reports that a number of people have been stabbed.
“It is really worrying,” said Ms Barrett.
“You hear from your child saying someone has been stabbed you don’t know what to do for the best.
“You just don’t expect it, you send your children to school and think they will be safe.
“It is comforting to know they are locked in the classrooms though.”
Mrs Barrett has said she has heard nothing from the school.
“It’s just a waiting game,” she said. “I don’t know whether to go down there or not.”