A former teacher at a prestigious high school in Adelaide has been jailed for at least two years for sexually exploiting one of her students.

Key points: Teacher Sonia Ruth Mackay wept as she was sentenced for sexually exploiting a student

Teacher Sonia Ruth Mackay wept as she was sentenced for sexually exploiting a student Judge said Mackay's offending was "unforgivable"

Judge said Mackay's offending was "unforgivable" She said the teacher breached the trust of the boy, her employer and the community

Sonia Ruth Mackay, 43, pleaded guilty to persistent sexual exploitation of a child in September.

The District Court heard she groomed a 17-year-old boy before having unlawful sex with him numerous times including at her house, at his family's home and in public areas including in a lift and in a city car park.

Judge Liesl Chapman said Mackay drank alcohol and smoked cigarettes and cannabis with the victim and bought him expensive presents.

"In light of what you were doing and the way you were doing it, it is evident to me that you could not have been thinking straight," Judge Chapman said.

"You seemed to have lost touch with reality and were living in some sort of fantasy land."

Judge Chapman said Mackay's offending had a devastating impact on the victim and his family.

"The victim's mother said she does not pity you because you are a grown woman, a teacher, a mother and a wife who she says manipulated her son's emotions to meet your own selfish needs," she said.

"Your behaviour causes a feeling of outrage, quite rightly, in the community.

"Your behaviour was manipulative and unforgivable."

Student should have been 'safe' at school

Mackay wept as she was sentenced to four years and five months in prison.

The court heard a psychiatric assessment found Mackay was at a low risk of sexual reoffending and that she was sorry for the pain and suffering she had caused her victim and his family.

However, Judge Chapman said suspending the sentence would not adequately deter others from engaging in such behaviour.

"It was an emotionally charged and sexually intense month, I take into account that your victim was at the upper end of the age range for this offending… and it was close to end of his time at the school."

"Nevertheless, he had been your student that year… he should have been safe at school, there to develop and mature in his own time."

She said Mackay's offending was a gross breach of trust.

"You breached the trust of him as a teacher, you breached the trust of his parents and siblings… you breached the trust of your employer, you breached the trust of the school community."

Judge Chapman said she understood "jail would be difficult and crushing" and imposed a non-parole period of two years and one month.

"In all of the circumstances I think you would benefit from a long time on parole," she said.

As she was taken into custody, Mackay told her family who were visibly upset, that she loved them.

Dreams 'shattered' and 'stolen'

During a pre-sentencing hearing, the court heard emotional victim impact statements from the teenager and his parents.

The boy's mother told the court Mackay had asked for her son's mobile phone number under the guise that she was helping him with his school work.

She said Mackay exploited her son and stole his innocence.

"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," she said.

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

The court heard Mackay had sent the victim sexually explicit text messages and that his DNA was found on sheets at the home she shared with her husband and young children.

In a statement read to the court, the victim said he felt ashamed and embarrassed about what happened and 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.