The inquest heard that Gareth was diagnosed with high functioning Autistic Spectrum Disorder when he was five and had specialist help throughout his pre-16 schooling, often on a one-to-one basis
Earlier this week, Mrs Oates told the inquest how Gareth had been bullied at secondary school but this was dealt with.
Things got worse when he started at college, partly because he travelled independently and was targeted by youths on the train and in other public places.
Administrator Mrs Oates said she had later received an apology from Suffolk Police for not dealing with this more robustly.
She said her son found the transition to college from school difficult for a range of reasons.
Although the college put a number of measures in place to help, she believed it was not enough.
In the summer of 2009 the taunting caused Gareth to run out of college into a wood and phone his mother her saying: "Mum, I'm going to kill myself".
His mother explained to the coroner how a month after this she found a message on her phone from her son saying he was on top of cliffs at Sheringham, Norfolk, preparing to jump.
She said the message said: "This is the last time you'll hear my voice."
Mrs Oates described how she became more and more concerned about her son's suicidal tendencies over the summer of 2009 but could not convince mental health services of the seriousness of his situation.
She told the inquest: "Nobody seemed to get their act together after he'd attempted suicide in July 2009."
She added: "Until I started to kick up a fuss, nobody did anything."
Gareth eventually started a course of cognitive behavioural therapy in September 2009.
His mother described how he became obsessed with the 1985 action film The Runaway Train - which ends with one of the main characters killing himself in front of the locomotive.
Mrs Oates said she believed some of the details of her son's death mirrored that in the film.
She told the coroner she believed her son travelled to the Huddersfield area because he had once been obsessed with a DVD about the last days of steam engines in the Pennines, which featured the spot where he died.