A Victorian court has heard allegations school principal Malka Leifer told a former student "this will help you for your wedding night" while sexually assaulting her at a school camp.

Warning: This story contains details of allegations of sexual abuse.

Mrs Leifer is facing 29 charges at the County Court of Victoria, including rape, sexual penetration of a child aged 16 or 17 and indecent assault.

She is accused of sexually assaulting three sisters Dassi Erlich, Nicole Meyer and Elly Sapper.

The ABC has received permission from the sisters to use their names.

Mrs Leifer has pleaded not guilty to all charges.

On the first day of the trial, Crown Prosecutor Justin Lewis began by making an opening statement to summarise the Crown's case against the accused.

He told the jury five of the charges related to alleged acts against Ms Myer, 14 charges were in relation to alleged acts against Ms Erlich and 10 charges related to alleged acts against Ms Sapper.

Mr Lewis told the court that growing up, the sisters were from a large family where their home life was difficult.

"Their mother suffered borderline personality disorder and was verbally and physically abusive to them," he said.

Mr Lewis said each of the sisters attended Adass Israel School, where the accused began teaching in 2001 after moving to Melbourne from Israel as the head of religious studies.

"She had the final say over many school matters and was a very persuasive person and well respected in the community," Mr Lewis said.

Mr Lewis described the three sisters as being raised in the ultra-orthodox Hasidic community, where they were not exposed to television, radio, magazines or the internet within their home.

He said women within the community were encouraged to dress modestly and were discouraged from having any kind of relationship with men outside of their families, once they were over the age of three.

Mr Lewis said the complainants had explained that women in their community were only provided with sex education in the lead-up to their wedding.

"The three complainants did not have any knowledge or understanding of sex during the period of the alleged offending," he said.

Mr Lewis told the jury that Mrs Leifer would have favourite students at the school who she treated differently, and Ms Meyer was one of her favourite students.

He told the court Mrs Leifer started organising to meet Ms Meyer alone, while she was in year 11, and this was when the accused began touching her student.

He said Mrs Leifer would touch her student's neck and face and "on some occasions she undid her bra and fondled her breast under her bra".

Mr Lewis told the court when Ms Meyer returned to the school in 2003 as a year 12 student, Mrs Leifer had become school principal.

He alleged Mrs Leifer continued to touch Ms Meyer when the student was asked to attend the principal's office alone.

In 2004, Ms Meyer started working as a teacher at the school.

While in that role, the prosecution alleges that Ms Leifer abused Ms Meyer both at the school and at the accused's home.

The court heard Mrs Leifer would tell Ms Meyer that she loved her and not to tell anyone about what they were doing.

Ms Meyer "felt too scared to tell people or ask the accused to stop", Mr Lewis said.

The prosecution allege that Mrs Leifer went on a school camp in 2006, that Ms Meyer was also attending.

During the camp, the prosecution said, they were both in the same room when the accused started touching Ms Meyer, digitally penetrated her and then said "this will help you for your wedding night".

The prosecutor alleged Mrs Leifer raped Ms Meyer a second time at the camp and on another occasion in her office at the school.

At a later school camp before Ms Meyer was to marry, the prosecution alleged Mrs Leifer and Ms Meyer were sharing a bed, and that Ms Erlich was also sleeping in the same room.

The prosecutor alleged that Mrs Leifer got on top of Ms Meyer when she thought Ms Erlich was sleeping and touched her.

He said Ms Meyer had "no idea what the accused was doing because she had no knowledge about sex" but she did know it "made her feel scared and uncomfortable".

Court hears allegations of sexual assault against second sister

The County Court also heard the prosecutor's allegations that Mrs Leifer sexually assaulted Ms Erlich.

Mr Lewis said when Ms Erlich was a year 10 student at the school, Mrs Leifer pulled her into her office and "said she knew what was going on at home with her mother and she could go to her for support".

At that time Ms Erlich was 16 and began attending private lessons at Mrs Leifer's home about "Jewish morals and how Jewish girls are supposed to act", the court heard.

Here, the prosecution says, the accused would rub her hands on Ms Erlich's thigh and inside her skirt and "would ask what was happening in her life and repeatedly told her she could trust her".

The prosecutor said on one occasion at Mrs Leifer's home, the accused was touching Ms Erlich when she told her "to call her 'mother' and said this is how much she loved her".

Mr Lewis said Mrs Leifer cradled Ms Erlich "like a baby" while touching her.

The prosecution said during the lead-up to the winter year 11 camp, the accused would arrange for Ms Erlich to attend her office at the school where she would touch her student, including her breasts and genitals.

At the school camp in Rawson Village, the prosecution alleges in the last few days Mrs Leifer pulled the complainant away to her bedroom and "undressed her until she was almost entirely naked".

The prosecutor said Mrs Leifer made Ms Erlich stand up, touched her breasts and sexually assaulted her.

The prosecution also alleges Mrs Leifer used her daughter's room to rape Ms Erlich when she stayed the night at the accused's home, before she married, and that in 2006 Ms Sapper walked in on Mrs Leifer touching her sister at the school.

Mr Lewis outlined to the court the Crown's allegations in regards to the third complainant, Ms Sapper.

Mr Lewis said in 2006 when she was in year 12 Ms Sapper began doing errands for Mrs Leifer and "felt she could trust her".

It was during the period Ms Sapper was involved in a school play that the prosecution alleged Mrs Leifer organised to meet her alone, where she touched her breasts and asked "does it feel good?".

The prosecution allege this touching was repeated on the first night of the school play and continued in 2007, when Ms Sapper began helping as a teacher, even though she was only 17.

The Crown alleges that throughout 2007, Mrs Leifer would organise to be alone with Ms Sapper where she would touch her.

Prosecutors also say Mrs Leifer on one occasion took Ms Sapper to bed where she used a sex toy and then her finger to sexually penetrate her before compelling Ms Sapper to penetrate her.

Mr Lewis alleged that Ms Sapper did not consent to any of the sexual acts and told the accused to stop on every occasion, and she would either not respond or say "this is good for you".

Defence lawyer tells court 'central issue is whether these sexual acts occurred'

The prosecution explained that the allegations first surfaced after Ms Erlich disclosed abuse to a counsellor in Israel in 2008.

Barrister Ian Hill, KC, also addressed the jury, representing Mrs Leifer.

He explained that the defence would not yet argue its case, but could respond to the allegations.

Mr Hill told the jury the "critical issue in the trial, the central issue, is whether these sexual acts occurred at all".

He said each charge was denied and the "credibility and reliability" of the witnesses would be central to the case.

Mr Hill said further to this, 21 of the charges were said to have occurred "at times when the respective complainants were legally capable of consenting".

He explained it would be for the prosecution to establish that the complainants had not been consenting.

The barrister also told the court that the defence would dispute that the complainants "were ignorant of sexual matters … not withstanding their ultra-orthodox upbringing."

Mr Hill flagged with the jury that another issue in the trial will be whether "collusion or contamination" of evidence has influenced the case.

Mr Hill said in the case of Ms Meyer, her "accusations about Mrs Leifer have evolved over time", saying when she first gave a statement to police in 2011 she did not include any allegations of rape.

Mr Hill encouraged the jury to keep an open mind until they heard all of the evidence.

The trial continues.