A teacher at Kings' School in Winchester collapsed and died in front of pupils sitting their GCSE exams.
The woman, who was in her 40s and a long-serving member of staff, suffered a medical emergency shortly after students arrived for the day.
An air ambulance carrying a doctor and two advanced paramedics landed at the school at 8.58am on Thursday.
Hampshire Police confirmed they were called by ambulance colleagues an hour later.
The woman was pronounced dead at the scene.
Around 1,800 students attend the highly-rated school, which immediately went into lockdown.
Police said the death is not being treated as suspicious and a file is being prepared for the coroner.
The woman's next-of-kin have been informed.
Following the emergency, the school sent an email to parents explaining that pupils would be dismissed early due to the ongoing situation.
The school remained closed on Friday after the teacher's death
|Year 11 examinations continued as scheduled despite her death.
"All pupils are safe and remain supervised. We are now beginning a controlled dismissal process," the email said.
The school remained closed on Friday as well.
Hampshire and Isle of Wight Air Ambulance confirmed its team was deployed by helicopter to Winchester that morning
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Dozens of floral tributes, candles and cards were placed at the school gates the next day.
Hundreds gathered to pay their respects to the teacher, identified locally as Mrs Bamford, who served as the school's head of business and computing.
One pupil wrote: "You were a wonderful teacher and will forever be remembered. Thank you for always being kind."
Another card read: "You were such a sweet, kind, lovable, enjoyable and free soul. You would never ever hurt a fly."
On social media, one former student wrote: "Thank you for being the kind of teacher that inspired and taught with kindness and compassion."
Another tribute read: "One of the kindest and caring teachers. We are completely devastated by this news."
One pupil described Mrs Bamford as "a beautiful lady who just had a lovely aura about her. Always smiling."
A spokesman for Kings' said: "Our focus remains on supporting the family, our staff and pupils at this difficult time."
The school went on to requested that its privacy be respected.