An Adelaide teacher who admitted to sexually abusing one of her students has broken down while apologising to his parents in court.

Sonia Mackay, 43, faced the South Australian District Court on Wednesday after pleading guilty to the persistent sexual exploitation of a child in 2017. The former English teacher, who worked at Christian Brothers College, is facing life behind bars.

Reading a letter of apology, Mackay said she was “so ashamed” and “deeply sorry” for her “gross breach of trust”.

“I am deeply regretful of my actions,” she said. “Through my indecent actions I have brought great distress to (the victim) and his family.”

The court also heard statements from the boy and members of his family this morning.

In a victim impact statement, the boy’s mother told the court Mackay had called her and asked for his phone number under the guise of helping him with his school work.

The mother said she became worried when her son stopped coming home for days at a home.

“I had no idea where he was sleeping, 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 boy’s mother recounted one incident when he did come home and Mackay called him and threatened self harm.

“I saw my son terrified... he believed it was his fault for leaving her alone,” she said.

Mackay, from Henley Beach in Adelaide, was arrested by detectives from the Special Crimes Unit in December last year.

After Mackay’s arrest, a letter was sent home to parents informing them of her suspension from the private school.

Under state law, the age of sexual consent is 17, but that increases to 18 if one of the parties is in a position of authority over the other.

In September, Mackay pleaded not guilty to two aggravated counts of indecent assault, and one count of unlawful sexual intercourse, involving a second, separate boy, the Adelaide Advertiser reports.

Mackay’s identity was suppressed until her guilty plea, when the suppression lapsed.

All three offences are alleged to have been committed last year in the southern suburbs.

The case, before Judge Liesl Chapman, will return to court in December.

megan.palin@news.com.au | @Megan_Palin