An "intelligent", "loving" and "caring" 13-year-old boy who was found suspended from a pull-up bar in his bedroom doorway died through misadventure, an inquest heard.
Harry Rock died on March 20 2017 in an "inadvertent suspension using exercise equipment", coroner James Healy-Pratt ruled at Eastbourne Coroner's Court.
The teenager, from Eastbourne in East Sussex, had completed one of his bi-weekly tutoring sessions that Monday morning, a few hours before his mother found him hanging in the doorway of his bedroom.
Amanda Rock, who had a hairdressing business at home, checked up on the lesson in her son's room before she started work with a client at around 10am.
After the client left at around 1pm, Ms Rock said she climbed to the top floor to Harry's room.
She told the inquest: "As I reached the second flight of stairs, I almost walked into him and I knew exactly what I was looking at.
"I thought it was a joke at first because I thought he was smiling, but then I realised it was his tongue."
Ms Rock found her son suspended by his dressing gown sash, which was caught around his face and under his chin, and a "rickety chair" was found tipped onto the floor.
The inquest heard that Ms Rock shouted for help and eventually managed to cut the teenager down from the exercise bar after dialling 999.
She performed CPR while paramedics were on the way and Harry was taken to Eastbourne District General Hospital, where he was pronounced dead. The medical cause of death was suspension.
His mother said: "I believe he was doing whatever exercise he was doing, the chair tipped and the sash restricted him.
"I truly believe it was an horrific accident."
Harry's GP, who was not at the inquest, said in a written statement read out to the court that he had "very little in the way of medical history" and there was "no mention of mental health issues".
The court heard that Harry's tutor, Rowanne Brown, noticed a change in his behaviour in February 2017, which she described as "teenage angst".
She said: "I was finding that having to learn so much and having to put so much effort in was causing him distress."
On her last lesson with him, the tutor told the inquest that he "looked visibly upset" at one point, and he discussed being left out of a holiday which his dad and stepmother had arranged with their other children 18 months prior.
His mother told the coroner that this exclusion "played on his mind".
Daniel Dugan, a detective sergeant who attended the scene, said there was no evidence on the student's phone or social media that he was suicidal, and said officers did not recover a suicide note.
The coroner said: "This was a tragic experiment that went very wrong, but it certainly wasn't suicide."
Harry, who was affectionately nicknamed "Bear", loved cats and gaming, and had been home-schooled due to his advanced academic ability.
He was undergoing tutoring for his upcoming GCSE exams, just weeks away, and aspired to go to college, his mother said after the inquest.
Ms Rock said: "He was fun, loving, caring - he'd always open the door for you. He was a gentleman, not loud, not lairy."
She said she was "totally in agreement" with the coroner's ruling of misadventure.
"He's a boy doing boy stuff," she said, adding that Harry desired a six-pack.
She said: "I was blessed to have him for 13 and three-quarter years, and now he's gone home."
A fundraising page has been set up by Harry's family in his honour at harry-rock.muchloved.com, and funds will go to Cats Protection and You Raise Me Up, a charity supporting families who have lost young adults.