A teacher at a prestigious Adelaide school who sent a student sexually explicit messages and encouraged him to meet her for sex has avoided jail.

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 in the District Court last month.

The court heard Schmoock sent the student sexually explicit messages via Skype and Whats App, in what started out as counselling but developed into an inappropriate relationship.

Judge Gordon Barrett said Schmoock's offending escalated when she booked a cottage in the Barossa Valley and asked the student to meet her there to have sex.

"You burdened him with the prospect of you losing your career, your marriage and even your life if he were to disclose the communications you were having," Judge Barrett said.

"You were reckless about the effects on him of your seeking a sexual relationship."

Pages of messages Schmoock sent to the student were tendered to the court, including some where she tells him that she loves him "from the bottom of her heart" and admits her wrongdoing.

"I acknowledge that I should never have engaged with u in an adult love relationship as u cannot handle the less than perfect parametres of this one – I'm sorry I'm not 20 and single," Schmoock said.

In other messages, Schmoock tells the student to keep quiet about their relationship.

"There's 2 ways this can go: 1. Nowhere 2. Everywhere: u just need to keep ur mouth shut." "We could love each other in secret until u finish skool." "I'm not going to beg. If you are man enough to take me on, do it now."

In a victim impact statement read to the court during sentencing submissions, 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."

Judge Barrett agreed to suspend a 22-month jail sentence on a $1,000 bond to be of good behaviour for three years.

He said Schmoock was suffering was a mental illness at the time, was at low risk of reoffending and was remorseful for her actions.

"You have no prior convictions, this offending is different to most types of this offending which come before the court," he said.

"You are acutely aware of the harm you have done and you are receiving treatment to prevent it happening again.

"You are remorseful and you have family responsibilities."

Schmoock will be eligible for parole in March next year.

The German national, who has a husband and two children in Australia, could face deportation as a result of being sentenced to a suspended jail term greater than 12 months.