Ella Pallister was a student at Thomas Hardye School in Dorchester.
In a statement the school said: "We are devastated by the news of the tragic and sudden death of Ella Pallister.
"She was studying in Year 13 and she was a popular, bubbly, hard- working and caring student.
"Her closest friends are in shock, but the whole sixth form and school community are grieving for her loss.
"Our thoughts and condolences are with her family at this very sad time."