The teenager died in her sleep at Oswestry School and was found last Saturday morning in her dormitory at the independent school.
The Year 13 pupil has not been named by the school, which has asked for privacy and compassion for her family.
Oswestry School said it was supporting its pupils and staff and the girl's family in the wake of the tragedy.
A spokesperson said: "It is with immense sadness that we confirm the tragic news that a Year 13 pupil from Oswestry School passed away peacefully in her sleep on the morning of March 18.
"This is an incredibly difficult time for the whole school and our thoughts and prayers are especially with her family.
"Our priority is supporting our pupils and staff, and her family. We respectfully ask for privacy and compassion for the family and the school community during this painful time."
Oswestry School is an independent, co-educational day and boarding school for pupils between the ages of four and 18.