“The offender deliberately chose to offend time and time again in the way that he did for the depraved purpose of sexual gratification,” District Court Judge Kara Shead said at the time.

Lawyers for Younan argued in the NSW Court of Criminal Appeal his dementia and an assault he experienced while in custody reduced the need to deter him from reoffending.

But Justice Julia Lonergan on Friday upheld Judge Shead's sentence, finding her consideration of each aspect "transparent and consistent with principle".

Younan's "calculated lies" to the victim and police demonstrate he knew what he was doing was wrong, she said, undermining claims his mental health issues diminished his culpability.

Justice Lonergan also rejected the submission his sentence was manifestly excessive.

"He used his authority and access to her, in the context of trips away from her home for a sport she loved, in his sole care, and in a position of trust, to lie to her and manipulate her to accept what he was doing to her body was appropriate and 'good for her tennis game'," she said.

"She was too young, vulnerable and inexperienced to understand the betrayal of her trust, although she knows that now. 

"This was serious offending."

The repeated abuse over six months was uncovered after another student stumbled across the pair naked in a hotel room and called his parents.

Justice Lonergan's findings were supported by Justice Peter Hamill and Justice Mark Ierace.

Younan will be eligible for parole on November 3, 2026.

1800 RESPECT (1800 737 732)

National Sexual Abuse and Redress Support Service 1800 211 028