Kilvington Grammar School student Lachlan Cook, 16, suffered diabetes complications during a trip to Vietnam in September 2019 and later died in hospital in Melbourne.
He had been self-managing his type-1 diabetes when he fell ill and was taken to hospital 24 hours after first showing symptoms.
Lachlan suffered a heart attack and was flown back to the Royal Children's Hospital in Melbourne, with his life support switched off in October 2019.
A coroner found his death was preventable in 2023, with WorkSafe issuing charges to both the school and travel company World Challenge Expeditions.
Kilvington faced Melbourne Magistrates Court on Thursday, where it pleaded guilty to one charge under to the Occupational Health and Safety Act, relating to ensuring that persons other than employees are not exposed to health and safety risks.
The school's principal Rob French stood in court and said: "Guilty, Your Honour."
Kilvington was ordered to face the County Court for a pre-sentence hearing in December.
World Challenge Expeditions, which is facing three charges, is yet to enter a plea and its lawyers asked for a two-month adjournment.
The company will return to the court on September 20.
Outside court, Mr French confirmed the school's plea, but declined to comment further.
"As the matter is still before the courts, I am unable to comment further at this stage, other than to say that my thoughts and prayers remain with Lachie's family and friends, who continue to mourn his tragic loss," he said in a statement.
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