The school's legal team came out on top at the NSW Mock Trial Competition grand final after a heated debate with St John Paul College Coffs Harbour.

Chevalier College has now become the eighth school in NSW in the past 35 years to win the competition twice.

During more than three hours of intense legal argument, Chevalier College's legal team challenged the evidence of St John Paul College at Sydney University's College of Law Mock Court.

Barrister and Chevalier College's mock trial team coach Geoff Beveridge has coached the school's teams for the past three years.

He said the competition took a lot of commitment, including between five and 10 hours of research each week.

"From February, right through to December, in most cases, we meet at least twice per week and sometimes three times a week, so it's a lot of after-hours commitment," Mr Beveridge said.

"We treat it like a high court case."

As the prosecution, Chevalier College were tasked with proving beyond reasonable doubt the defendant Cassidy Mettich was guilty of consorting in accordance with Section 93 of the NSW Crimes Act 1990.

A panel of three judges including two non-judicial officers and a leading judge from Parramatta Children's Court listened to the arguments made by both sides and ruled on all the objections.

The performance from both sides had the ingredients of a true-to-life trial which had two barristers and an instructing solicitor.

Chevalier College's witnesses Brodie Ackroyd and Mariette Lewis adopted the role of senior police officers with lively characterisation.

Brodie said the win was a "team effort" and "a really good experience."

"For all of us the different talents we've learnt will carry on to our careers and futures," she said.

"The experience has been something I wouldn't have thought of doing but I've learnt so much. We're very thankful to our coaches and we're really proud of each other."