When Stuart Chaifetz secretly recorded his autistic son's school day, what most distressed him wasn't hearing staff shouting at 10-year-old Akian or calling him a bastard, it was the merciless way they mocked him, then ignored him as he cried.
Six months ago, Akian's New Jersey special needs school told Mr Chaifetz that his son had started acting up. He was having violent outbursts and hitting out at staff. The behaviour was so out of character that even a behavioural specialist who examined Akian couldn't explain it.
Mr Chaifetz decided to investigate himself. "I felt I was losing my son," he says. "I needed to know what was going on and this seemed like the only way to find out." One day in February, he dropped a $30 (pound;19) recording device in his son's pocket. That night, when he played back the six-and-a- half hours of audio, he was devastated by what he heard.
Throughout the day, the teachers and assistants in Akian's special needs class discussed being hung over, getting sterilised and having fights with their husbands. They shouted at the children for interrupting their conversations, made derogatory remarks about their parents, insulted and bullied them. One assistant told Akian to "shut your mouth".
When the school district failed to fire the teacher in charge of the class, Mr Chaifetz made a video with the worst of the audio clips. Last month, he posted it on YouTube. Within days it had risen to the top of social news site Reddit and attracted widespread attention.
Akian lives with his father most of the time. On the Friday that his father recorded the goings-on at school, Akian was about to spend the weekend with his mother. Because the separation from his father makes him nervous, he needs reassurance. In the most chilling clip, Akian is heard asking a member of staff: "Can I see Dad after Mum?" Her scornful reply - "You can't see" - is followed by laughter from a colleague.
Mr Chaifetz made the video, he says, to win back dignity for his son. He also wanted to bring attention to a system that gives undue protection to teachers with tenure, even those caught bullying vulnerable students.
With the unexpected attention his son's story has attracted, his video has now been viewed more than 4 million times, his inbox has filled up with thousands of emails from around the world and a New Jersey state senator has pledged to sponsor a bill to change the rules on teacher dismissal.
Akian is now at a new school and doing well. Cherry Hill school district is conducting a proper investigation. Mr Chaifetz feels some satisfaction. But he still struggles to understand how anyone could treat his son that way. He believes that because Akian and his classmates have limited verbal skills, the staff felt they could get away with doing and saying things they never would in a mainstream classroom.