A former teacher who was jailed for having sex with a student at a prestigious Adelaide high school has walked from court after successfully appealing against her sentence.

Key points: Sonia Mackay had sex with a male student while working as a teacher at an Adelaide school

Sonia Mackay had sex with a male student while working as a teacher at an Adelaide school She was sentenced to at least two-and-a-half years in jail

She was sentenced to at least two-and-a-half years in jail The Court of Criminal Appeal set aside her sentence in favour of a good behaviour bond

Sonia Ruth Mackay, 43, was five months into a two-and-a-half year non-parole period which began in December.

She was found to have groomed a 17-year-old boy before having sex with him several times, including at her house, the boy's family home and in public.

The Court of Criminal Appeal on Thursday set aside her sentence, instead fixing a new non-parole period of 16 months.

It was suspended and Mackay has been placed on a good behaviour bond.

Mackay pleaded guilty to her offending last year.

The District Court was told how Mackay had exploited the boy, having asked his mother for his phone number under the guise of helping him with his schoolwork.

"He didn't return home for days at a time. I had no idea where he was sleeping or who he was with, was he safe, or worse," the boy's mother told the court.

"When he attempted to come home she bought him expensive underwear and gifts so he had no excuse but to stay with her."

A statement was read to the court on the victim's behalf, where he said he felt ashamed and embarrassed about what happened, and he felt like he had lost two years of his life.

"My dreams were shattered and stolen from me … and I can now see how I was purely being used," he said.

Mackay declined to answer journalists' questions as she walked from the city court building.

Her three-year good behaviour bond includes several conditions.