A teacher at a Perth private girls' school has been jailed for almost five years for sexually abusing two of her teenage students after letting "her feelings overrule her brain".

The 35-year-old woman, who cannot be identified, pleaded guilty to 33 child sex offences committed between 2015 and 2017, when the two girls were aged about 15 and 16.

She was a drama teacher and the victims were both students in her classes.

The abuse happened over about 18 months, with the offences committed at the teacher's residence and at the homes of the girls, whose families had befriended the woman.

Teacher had 'deep cognitive distortions'

Her lawyer, Mark Andrews, told the District Court his client maintained the sexual offences were not her main motivation, but rather she had wanted "to advance the deep connection she had with the two complainants".

He said she developed "deep cognitive distortions" and believed she was in "a personal relationship" with each of the them.

"Having believed she had formed a relationship with them, she did not pause and stay within the proper boundaries," Mr Andrews said.

"She looked at them as friends rather than as students … she acted on emotion rather than logic. Her feelings overruled her brain."

Mr Andrews said his client accepted she had betrayed the trust put in her by the girls, the school and the families of the victims, and was "deeply ashamed".

"She wants me to apologise to each of the families for that gross breach of trust," he said.

State prosecutor Sharyn Bowman said the offences were aggravated by the age disparity between the woman and the girls — she was 31 when the abuse started, while the girls were about 15.

She also said the abuse, which came to light after one of the girls told a friend, happened over a lengthy period.

'You failed to recognise the boundaries'

Judge Mark Herron described the offences as "brazen", saying the woman had been trusted by the school and the girls' families to care for and protect them.

He said each of the victims was vulnerable and there was an element of "grooming" in what the woman had done, by taking advantage of them for her own sexual gratification.

Judge Herron highlighted aspects of the victim impact statements from the girls, in which he said they spoke "powerfully and eloquently" about being conflicted and confused about their feelings towards the woman.

The court heard one of the girls still felt a sense of loyalty towards her, while the other said she still cared deeply for the woman.

But both said their mental health had suffered and they felt a range of emotions from anger to sadness.

Judge Herron accepted the woman was remorseful and that she had lost her career as a teacher, but he said she had failed in her duty of care to the students.

"You failed to recognise the boundaries that must remain between a teacher and student … you were in a position of power and authority over them," he told her.

He sentenced the woman to four years and 11 months' jail.

She will have to serve two years and 11 months before she can be released.