A "caring and intelligent" teacher at a southern Perth suburban school has been sentenced to seven and a half years in jail for sexually abusing two teenage students.

Key points: The teacher targeted two students at her school, one who was just 13

The teacher targeted two students at her school, one who was just 13 She bought gifts for her victim including jewellery and a cat

She bought gifts for her victim including jewellery and a cat Her offences so serious they justified an immediate prison term, the judge said

The 29-year-old woman, who cannot be named to protect the identity of her victims, pleaded guilty to more than 40 charges relating to two girls, one of whom was in her class.

The offences were committed between 2015 and 2017.

The first victim was aged 13 at the time the offending began and the District Court was told the very first offence was committed in one of the classrooms at the school, which cannot be named.

It was the girl's first sexual experience and led to a "relationship" between the pair, with the teacher buying her gifts including jewellery and a cat.

The girl lied to her parents about going to the teacher's house and also reporting to the school principal when suspicions were raised about the nature of their dealings.

The court heard the teacher had threatened self harm if the girl revealed what was going on, which Judge Ronald Birmingham described on Friday as "manipulative and controlling behaviour".

The teacher built up trust with the students before exploiting that for her sexual gratification. ( ABC News )

The second victim was aged 17 and the abuse happened after the teacher struck up a friendship with her.

The court was told the woman would also send the girl messages of a sexual nature.

It was also revealed the teacher later began a relationship with a third student, but she was not charged with any offences over it.

Judge Birmingham said it was "indicative" of the woman's character that she seemed "focussed on having sexual relationships with young girls".

'Grooming, manipulating and corrupting' victims

Judge Birmingham said the teacher had "groomed" the victims by first building up a relationship of trust with the teenagers to seem like she was a source of comfort for them and to make them feel safe.

He said the teacher then took advantage and exploited the victims for her own sexual gratification.

Judge Birmingham said references provided to the court on the woman's behalf described her as "an intelligent, caring and capable young woman" with other teachers at her school finding it hard to believe she had committed the offences.

The teacher targeted two students, one of which was just 13 at the start of the offending. ( ABC News: Craig Berkman )

He also said he accepted that the woman was genuinely remorseful and that her life had now been "utterly destroyed".

But he said the offences were so serious that only an immediate term of imprisonment was justified.

"It was the abuse of vulnerable children, when you were in a position of trust," he said.

"You were manipulating and corrupting these young girls for your own sexual gratification."

The teacher will have to serve five and a half years before she can be released.

She was only taken into custody last week, meaning she will first be eligible for release in February 2024.