"The windows, the bare walls. It was that every day. Every single day. They put me in a room on my own, I was in isolation," says Casey, 16.
More than 200 pupils spent at least five straight days in isolation booths in schools in England last year, a BBC News investigation has learned.
Casey's school disputes the length of time he spent on his own and said he was "regularly disruptive".
The teenager says he was placed on his own after he contracted fibromyalgia.
He takes the painkiller Tramadol for the chronic pain condition.
More than 5,000 children with special educational needs also attended isolation rooms at some stage.
Dozens of them had education, health and care plans (EHCPs) provided for children with complex needs.