A teacher at a prestigious Adelaide school encouraged a student to meet her for sex and emotionally blackmailed him into keeping their relationship secret, the District Court has heard.

Bettina Schmoock, 42, was a teacher at Concordia College in Adelaide's inner south-east when she was charged with one count of communicating with the intent of procuring a child for sexual activity.

The charge is aggravated because she was in a position of authority over her victim at the time.

Schmoock changed her plea to guilty just before her trial was due to start last month.

The court heard she sent messages via Skype and text to the student, in what started out as counselling but developed into an inappropriate relationship.

Prosecutor Mark Norman SC said the school took steps to caution Schmoock and monitor the situation when it became apparent she was becoming "too close" to the student.

"The defendant knew very much better than to do what she did," he said.

"When she was cautioned and monitored by the school she then took steps to disguise her relationship with the complainant."

'Emotional blackmail pressured everything I did'

In his victim impact statement, the student said he felt entrapped in the relationship and emotionally blackmailed into keeping it a secret.

"At the time, I called the Kids Helpline a lot and remained anonymous to avoid mandatory reporting," he said.

"I felt like there wasn't any other option than to keep it secret because she said she would kill herself if anything happened to her job.

"The emotional blackmail pressured everything I did … I was always scared that I would accidentally reveal it and cause her to die."

Bettina Schmoock was a teacher at the prestigious Concordia College at Highgate. ( Concordia College website )

Mr Norman said the genesis of the offending was platonic and initially Schmoock was a positive influence on the student.

But he said it escalated to a point where she invited the student to meet her at a cottage to have sex.

"She persisted in encouraging the complainant to join her in the cottage even when the messages show he had indicated his unwillingness," Mr Norman said.

"Because of the booking of that cottage, because of her persistence, it cannot be said that it was mere fantasy.

"She was plainly disappointed with the complainant's reluctance to commit to her or a sexual act."

Hyper-manic episode was 'out of character'

Schmoock's lawyer Mark Griffin QC said his client was not a sexual predator and that she was suffering from undiagnosed bipolar disorder at the time of the offending.

"She is sorry and apologetic because she genuinely cared for [the victim] and developed an emotional connection with him where she was honestly and genuinely concerned for his wellbeing," he said.

Mr Griffin told the court his client had little memory of some of the messages because she was intoxicated at the time and cringed when she re-read them.

"It is clear from the psychiatric evidence that's before the court that Bettina Schmoock was in the throes of a hyper-manic episode," he said.

He called for the sentence to be low, highlighting that Schmoock had previously been an exceptional teacher and that the conduct was out of character.

"If it were not for the underlying mental illness she was then suffering, for which she was not being treated, it would not have occurred," he said.

"Sadly we cannot wind the clock back and undo those wrongs; Ms Schmoock wishes she could."

The maximum sentence for aggravated communicating with the intent of procuring a child for sex is 12 years' imprisonment.

Schmoock could face deportation to Germany if she is sentenced to a jail term of 12 months or more.