The woman, now 21, told the Sydney District Court she was "scared, very tense" and "didn't want to be there" when Cameron Peter White had sex with her in his unit in Sutherland in Sydney's south.

Mr White, 39, is on trial over his alleged sexual relationships with a male student and two female students from three Sydney school campuses where he worked as a teacher.

He has pleaded not guilty to one count of aggravated indecency, and multiple counts of aggravated sexual intercourse and sexual intercourse with a person under care, alleged to have occurred between 2007 and 2013.

On Thursday, the woman, who cannot be identified for legal reasons, told the jury Mr White was her year 9 geography teacher at the Georges River College at Peakhurst in 2010.

He left the school midway through the year and, in November, the pair became Facebook friends and engaged in online messaging.

She said the conversations became "flirty" and, in December 2010, he asked her to meet at Cronulla railway station.

He drove her to his unit where he took her into his bedroom, pushed her up against the wall, kissed and touched her. He then moved her to the bed and had sex with her.

Asked by prosecutor Michael Barr how she was feeling during the incident, she said: "I didn't want to be there, I was scared, I felt very tense."

She did not tell Mr White how she was feeling. She said he told her to "just relax".

She said she was 15 at the time and had not had sex before and it was painful.

Giving evidence via video link, she said Mr White dropped her at Sutherland railway station and she caught the train home. He later messaged her to check that she had arrived home.

They met several more times for sex before the student ended the arrangement before school returned in February 2011.

Mr White had returned to school as a sports teacher and took the student for fitness lessons.

The woman asked him for a reference she needed to apply for a course and he agreed to provide it on the condition they have anal sex, to which she agreed.

She cried as she described the sex to the court. She said afterwards he drove her back to the train station and handed her the reference, dated September 2011, as she got out of the car.

Mr White messaged her from time to time asking her to meet up but she told him she didn't want to, she said.

In 2015, she and the second female complainant had online conversations in which they revealed to each other that they had lost their virginity to Mr White.

Under cross-examination by Mr White's barrister, Lisa-Claire Hutchinson, the woman said she didn't tell anyone about the relationship at the time.

Mr Barr said there was no suggestion that Mr White had forced himself on anybody, with all three alleged relationships consensual.

However, it is an offence for a teacher to have a sexual relationships with a student under 18.

Mr White was a teacher at Woolooware High School from 2004 to 2009, the Peakhurst campus of Georges River College for periods in 2009 to 2011 and the Oatley campus in 2012 and again in 2014 to May 2015, when he was arrested.

The trial continues.

with AAP