More than 150 lives were lost in the Peshawar school massacre of December 16, 2014, the deadliest extremist attack in Pakistan's history.
One year on, those who survived now study in the same rooms where they huddled in terror as their classmates fell around them.
The majority of them were children, many of whom were in the auditorium with Subhan when nine attackers armed with guns and explosives went on a cold-blooded killing spree.
"I feel unable to function. I keep remembering everything," Subhan, a bearded, soft-spoken 16-year-old says.
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When he is alone, memories of the friends who died alongside him that day come crowding in, and he says he cannot fathom how quickly his life was shattered.
"I think about how I used to be with my friends," he says.
His parents also remember how he used to be, saying their confident, outgoing son was transformed by the hours-long siege.
"The slightest of things he takes as though a bullet hit him," says his father Subhan Uddin.
The auditorium is now a sports hall and soldiers stand atop recently fortified walls as children play on the green, expansive grounds below.
But the trauma has lingered, says Andaleeb Aftab, a chemistry teacher at the school who fled into a bathroom with other staff after gunmen opened fire on them in a hallway.
Aftab's son, 16-year-old Huzaifa, was among those who died in the auditorium.
In their last exchange, she said, he came to the staff room and asked her for pocket money.
Aftab was trapped in the bathroom until evening, listening for hours as the attackers blew themselves up one by one.
It was only after she was rescued that she learned her son had died.