Yesterday, at the North Shore District Court, he was sentenced to two years and one month in prison and criticised by his victim's mother and Judge Pippa Sinclair.
It was his first time before the courts on a sex charge.
The court heard that in February the girl started a new school.
The school and the specifics of the girl's special needs have been suppressed to protect her identity.
Dredge was working for a transport company that supplied a taxi service for special needs students and the teenager was one of his passengers.
According to the summary of facts the offending started in February with Dredge inappropriately touching the girl's bare legs and, over three months, progressed to him putting his hand inside the girl's pants and touching her genitals.
In May the girl sent the text to her mother revealing what Dredge had been doing.
Dredge was remorseful about his offending and "overcome with shame and guilt", his lawyer told the court.
"He described being riddled with guilt which was eating away at his insides, sleepless nights and about being worried sick about what hurt he had caused to the victim and her family."
Judge Sinclair said Dredge had clearly premeditated repeated assaults on the girl.
He also "minimised and rationalised" his offending when interviewed for a pre-sentence report.
She said: "This was a particularly vulnerable victim ... you were aware of that ... and you took advantage."
Dredge showed no emotion as he was sentenced, even when the impact statement written by her mother was read out.
"The biggest fear we have held for [our daughter] has been the potential for abuse ... Sadly we were unable to protect her from you," the mother's statement said.
"We believe you purposefully looked for someone you thought would not tell, or if they did, would not be believed. You perceived that [our daughter] would be unable to communicate your reprehensible actions to us. But [our daughter] did tell, and we did believe her."
Victim's parents struggle with guilt
When their daughter started a new school this year she was worried about going each day in a taxi. She was scared she would be dropped off in the wrong place and get lost.
"I bought her a cheap $20 cellphone from the supermarket and told her she could call me any time," her mother told the Herald.
"We told her taxi drivers were safe people, that they look out for others, that a taxi driver would never hurt her. How terribly wrong we were."
Her daughter learned to text message and mainly sent her mother shopping requests for lollies. But in May that changed.
"She sent me the text: 'Mum why does the taxi driver like to put his hands down my pants and touch my bottom?' I was so caught off guard, it was different to anything she had ever texted me about."
Her mother called the school, and police were brought in.
"I couldn't believe it was happening," the mother said.
"I felt so sad for her. I'm like her voice, her protector. To think of her in that taxi by herself with this man doing things to her and me not being there to be her voice and make it stop ... It was pretty horrible.
"We, as parents, have struggled with immense feelings of guilt -- guilt over the reassurance we initially gave her when she expressed apprehension over catching a taxi to her new school."
The girl's father said they decided to speak about the case to protect other children.
"The main point is to try and stop it happening to other kids."
They do not blame the transport company that hired Dennis Dredge.
"They have apologised to us. We don't hold them responsible, you can't hold a company responsible for a single person's actions," said the victim's father.
