The Victorian parents of the 12-year-old girl who was told to dive into a pool that was too shallow, rendering her quadriplegic, have criticised the penalty for the swim school company.

Milly Yeoman was among other Year 6 students in the 'learner pool' at Swim and Survival Academy in Ballarat when she suffered the "catastrophic" and "tragic" lifelong injury in November 2016.

De Kort Enterprises, which owns the swim academy, was convicted and fined $150,000 in the County Court today after pleading guilty to failing to ensure the girl was not exposed to risk.

Milly’s parents scoffed as the sentence was read out, and left the courtroom quickly.

Outside court, they told 9News the fine “nowhere near enough”, and they hoped it would be $1,000,000.

The maximum financial penalty for the charge is $1.4 million.

Milly Yeoman was rendered quadriplegic in the incident. (9news)

Children routinely dived into the pool's northern end, but the water depth was below the minimum 1.5 metres recommended for diving, the court heard.

Milly was also much taller and heavier than most girls her age, and the academy should have been aware of this.

"She went straight down, hitting her head on the tile floor of the learner pool," County Court Judge Paul Lacava said.

"She sadly suffered spinal injury, rendering her quadriplegic for life."

Judge Lacava said the girl's life, and that of her parents and brother, had been "turned upside down by this tragedy".

"The impact is immense, touching upon almost every aspect of their everyday life," he said.

The court heard Milly's life had been "turned upside down by the tragedy", which occurred when she was 12 years old. (Nine/Supplied)

The company's directors, Rob and Julie De Kort, have spoken of their sincere regret and remorse for what happened in a statement to the court.

"And they speak of the steps they have taken to ensure that a similar incident does not happen again," Judge Lacava said.

The judge said a "significant" fine was needed to send a message that children must be protected at swim schools.

"This is a serious example of what is a serious offence," he said.

"The risks of diving into shallow water are regrettably well known.

"Grade 6 school children cannot be expected to fully understand that risk and so the academy had to take all reasonably practicable steps to protect them.”