A teenage arsonist torched the art block at his former school in revenge for being expelled.
The 16-year-old boasted about what he had done on YouTube saying police did not have any evidence to prove that he did it.
The blaze caused £260,000 of damage at Oakmeeds Community College, Burgess Hill.
The youth was caught after a former friend told police the teenager had called him at 1.17am saying he was standing outside the school watching it burn.
Art work pupils had spent months preparing for their GCSE exams was destroyed in the inferno on November 23, 2008 A mobile phone recording of him boasting how he had started the blaze was given to detectives a month later.
The teenager was yesterday found guilty of arson with intent to destroy property.
A jury at Hove Crown Court heard details of the teenager's disturbing past.
He was twice excluded from a previous school for starting fires.
He set fire to a piece of paper during a lesson and then tried to burn to a plastic chair as classmates watched.
He was suspended for three days but set fire to paper towels in the boys' toilets just days after he was allowed back again.
He was suspended again but his mother withdrew him from the school and he was found a place at Oakmeeds instead.
Headmaster Colin Taylor said the boy had a record of disruptive behaviour while he was at the school.
He was involved in 99 recorded incidents at Oakmeeds before he was finally expelled for good.
Ryan Richter, prosecuting, said the teenager later returned and exacted his revenge by starting the inferno.
There was no forensic evidence to link him to the blaze and police were never able to prove that he was the hooded figure seen walking away talking on a mobile phone as the flames took hold.
However, mobile phone records and a hotmail account he used to reply to YouTube comments accusing him of being responsible linked him to the blaze.
The teenager claimed he was at home all night and did not start the fire.
He said it felt “cool” to be arrested in front of classmates at the new school he went to after he was thrown out of Oakmeeds He claimed he had a reputation to live up to after his arrest and told other teenagers what they wanted to hear when he was recorded bragging about the blaze a month later.
He told the jury: “I said it but it was not true. I had an audience ready to listen to what I had to say.
“I felt like a little celebrity with these people standing round listening to me.”
The defendant was released on bail until he is sentenced on May 20.
Recorder Peter Gower, QC, told him it was likely he would be sent to a youth custody centre.
He added: “This was a deliberate attempt to set fire to the school and to cause substantial damage.
“You have been convicted on the clearest possible evidence and the most likely outcome is that you will be deprived of your liberty.”