Twelve children were injured, four seriously, when a heating duct collapsed in a college's sports hall during an exam.
The Year 9 pupils were hurt at Minster College, Minster Road, Sheerness, at about 0920 BST.
Emergency teams took 12 pupils, including four with serious head, neck and back injuries, to Medway Hospital.
Kent Fire and Rescue Service (KFRS) said it was "very lucky" the duct fell between rows of pupils.
About 150 students were in the sports hall sitting a Certificate in Preparation for Working Life exam when the metal heating duct fell from the ceiling. Eleven adults were in the hall at the time.
South East Coast Ambulance Service said four patients had serious neck, head and back injuries, but none was believed to have suffered life-threatening injuries.
A small number of people were treated at the scene for shock.
Sam, 14, was in the sports hall at the time of the incident and saw his friend get hurt.
He said he heard a noise and looked up moments before the heating duct fell down.
"I saw my friend was hurt and I moved the desks to get to him," he said. "I rang the ambulance and then my mum to tell her what happened.
"I am upset and I feel bad about my friend - all I can picture is him sitting there."
Medway NHS Foundation Trust in Gillingham said injured pupils were being treated and their families were at the hospital.
Head teacher Alan Klee said: "We were very lucky indeed.
"Most of the students have escaped with just cuts and bruises and are being discharged from the hospital as I speak.
"It's very fortunate that it fell between the desks so it missed many of the students.
"Nevertheless we have been very, very shocked by what has happened."
He said the sports hall received regular maintenance checks and the safety of the building had never posed any cause for concern.
"Twelve first aid-trained staff dealt with injuries immediately and emergency services were on site within a few minutes," he added.
Four of the Year 9 students suffered serious head, neck or back injuries
The school was closed after the incident.
A spokesman for Kent Fire and Rescue Service, which sent three appliances and a search and rescue team to the scene, said crews were called at 0918 BST
Kent County Council's education boss, Rosalind Turner, said: "Our thoughts are with the children and their families and we wish them all the best for a speedy recovery.
"We are working with Minster College to help staff and will be on hand to support the students and their families.
"The school will be open tomorrow to minimise disruption for those taking their exams."
'Everyone cried' after duct fall
Minster College on the Isle of Sheppey has about 1,600 students aged between 14 and 19.
It is due to merge with the Cheyne Middle School and reopen in September as the The Isle of Sheppey Academy, based on the two sites.
Some buildings at the two schools will be demolished and others refurbished in time for the new term but Kent County Council could not confirm whether this included the gym.