"The bus has been taken away and examined and there were no mechanical faults. So we are still hoping to find that driver."
Mr Shields said police were looking in to whether anybody was criminally responsible for the crash.
"We spoke to the driver at the time and he gave a statement. We have the driver's version of what happened but there may be another person involved, and until we speak to that other person we won't be able to know 100 per cent exactly what happened."
The group of about 50 Year 10 students was on its way to an overnight tramp to the Pinnacles Hut, in the Coromandel Forest Park, when the bus veered into a ditch.
Principal Iva Ropati said parents of the students involved in the crash were "distraught" when they heard about the crash.
A parent of one of the children injured in the crash said she was disappointed she found out about the crash through the media.
"I firstly phoned the school after I had seen it on the media, and we hadn't been contacted by the school. They said to me that they were waiting for more facts.
"The only contact the school made was to send a general email out to say there had been an accident with the students who had gone out."
She had initially waited at Howick College for her daughter to arrive because she said she was told her daughter wasn't injured and would be coming back earlier.
"The bus arrived 20 minutes later and my daughter wasn't on board ... I just lost it, I totally cracked."
She only found out her daughter was in hospital when a friend went to pick up their child from Thames Hospital.
The woman said her daughter was sitting next to the window on the side where the bus had fallen.
"Everyone who was sitting on the opposite side had landed on top of her. She's bumped and bruised which is expected. At the time she had head injuries.
"Her neck and her back are really sore."
She said she had spoken to principal Iva Ropati this morning, and he was very apologetic.
"I sympathise with what went down and I understand the stress the staff were under but there are protocols you take. Any parent will know that.
"I just want some guarantees in place that if anything like this ever happens again no parent has to go through this."