That's what Coroner Audrey Jamieson found after investigating the death of Kilvington Grammar School student Lachlan Cook.

The 16-year-old, from Bentleigh in Melbourne's southeast, had been self-managing his Type 1 diabetes on a World Challenge-led school trip to Vietnam in September 2019.

A few days into the trip, he began repeatedly vomiting and having stomach pain after a night eating street food in Hoi An.

But he was only taken to hospital 24 hours later when his vomiting wouldn't subsist and his blood glucose levels became dangerously high, Ms Jamieson found.

Lachlan's condition quickly deteriorated and he had a cardiac arrest while in intensive care.

He was flown back to the Royal Children's Hospital in Melbourne but was declared brain dead and his life support was turned off on October 4, 2019.

An autopsy revealed his cause of death was brain damage in the context of diabetic ketoacidosis.

Lachlan's abdominal pain and vomiting could have been caused by food poisoning, although that could not be determined during the autopsy.

Ms Jamieson on Wednesday ruled his death was tragic and preventable.

"There is clear and cogent evidence that the failures and shortcomings of World Challenge Expeditions and Kilvington Grammar School contributed to (Lachlan's) death," the coroner said.

The two Kilvington teachers on the trip, along with the World Challenge leader, were not trained to support students with diabetes, Ms Jamieson found.

They also did not have access to Lachlan's diabetes management and action plans, and there were no co-ordinated meetings around his health condition before the trip.

The 16-year-old was instead expected to monitor his own blood glucose levels and manage his symptoms, even as he became more and more unwell.

"(Lachlan) was generally capable of managing his diabetes adequately on his own," Ms Jamieson said.

"But I also find that his ability to manage his own condition declined when he became ill."

The coroner did not make any recommendations to Kilvington Grammar, noting there had been no incidents related to the management of Lachlan's diabetes while he was at school or on a school-run camp

She instead made four recommendations to World Challenge, advising the organisation to update procedures for students with medical conditions like diabetes.

Lachlan's mother Kirsten McMahon said the finding that his death was preventable was heart-breaking.

"We can only hope that other schools and camp providers learn from our experience," she told reporters outside court.

"All families should have the confidence that when their children participate, they will return back home and into their arms, healthy and safe."

A Kilvington Grammar spokeswoman said the findings were challenging and difficult to hear, and the school's thoughts and prayers remained with the Cook family.

The school had also implemented a number of restorative practices since 2019 and would continue to ensure the safety of its students domestically and internationally, the statement read.

World Challenge said it constantly reviewed and updated its health and safety procedures, and would continue to do so as they implemented the coroner's recommendations.

"We remain absolutely committed to working with schools, our partners and families to make school trips as safe and inclusive as they can be," the statement read.

Lachlan's family last year launched a civil case in the Victorian Supreme Court, claiming Kilvington Grammar and World Challenge breached their duty of care.

Those civil proceedings are still ongoing.

Australian Associated Press