The water bottle theory that could determine what caused the Sydney school crash.

As a shell-shocked Banksia Road Public School community reels from the loss of two of its students after a car ploughed into their classroom, one question is on everyone’s lips: how could this have happened?

The driver of the Toyota Kluger that crashed into the classroom on Tuesday morning, injuring at least a dozen students, two of whom died from their injuries, was 52-year-old mother-of-four Maha Al-Shennag.

Police say Al-Shennag underwent mandatory blood and urine tests, but no charges relating to driving under the influence have so far been laid. No one has suggested the act was intentional.

Now, a theory has emerged as to how the crash could have been caused by a distracted Al-Shennag.

The Daily Telegraph reports police are investigating whether the woman may have been reaching down to retrieve a water bottle she had dropped when the crash occurred. It is believed she may have accidentally put her foot on the accelerator.

This isn't the only question police will be asking Al-Shennag, who has been charged with dangerous driving, negligent driving occasioning death, dangerous driving occasioning grievous bodily harm and cause actual bodily harm by misconduct.

It's reported police will also explore whether the school mum may have been using her phone at the time of the crash, by examining data from her mobile phone.

They will also try to determine if the crash resulted from a fault in the car, by examining mechanical data from the vehicle.

Al-Shennag has been bailed to appear at Bankstown Local Court on November 29.

Meanwhile, tributes continue to be laid at Banksia Road Public School's gates as the community mourns eight-year-old students Andrew and Jihad. The boys were taken to Westmead Children's Hospital where they died from their injuries.

Two eight-year-old girls were also taken to Westmead in a stable condition, and one nine-year-old girl was taken in a serious condition.