The jury in the Malka Leifer child sex abuse trial has retired to consider its verdict, after hearing evidence over a six-week period.

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

Mrs Leifer, the former principal of the Adass Israel school in Melbourne's south-east, has pleaded not guilty to 27 charges against her.

Prosecutors allege Mrs Leifer sexually abused sisters Nicole Meyer, Dassi Erlich and Elly Sapper in secret between 2003 and 2007.

County Court Judge Mark Gamble told the jurors they can only find Mrs Leifer guilty if the allegations are proved "beyond reasonable doubt".

"You are the only ones in this court who can make a decision about the facts," he told them.

The jury now has the task of considering evidence heard over the last six weeks, and to deliver verdicts on each of the 27 charges.

Mrs Leifer is facing charges of rape (10), indecent assault (10), penetration of a 16 or 17-year-old child (3), indecent act with a 16 or 17-year-old child (1) and one count of compelled rape, where prosecutors allege she forced one of the complainants to perform a sex act on her.

Earlier in the trial, she was acquitted of two counts of indecent act with a 16 or 17-year-old child, because the laws used to charge Mrs Leifer came into effect after the alleged offending occurred.

During the case, the jury heard evidence from the sisters, police, psychiatrists and school staff.

The court was told Mrs Leifer was a well-respected figure at the Jewish school and within the ultra-conservative Adass Israel community in the early 2000s.

Allegations against her were raised in late 2007 or early 2008, when Ms Erlich made disclosures to a social worker in Israel.

In the months and years that followed her two sisters also claimed Mrs Leifer had sexually abused them.

The sisters allege the offending took place on school grounds in locked staff offices, on school camps and at Mrs Leifer's home.

Other than the sisters themselves, none of the witnesses at the trial testified seeing the alleged abuse take place.

Crown lawyer Justin Lewis argued Ms Meyer, Ms Erlich and Ms Sapper were credible witnesses, who had given "lengthy and detailed accounts".

Mrs Leifer's legal team did not call any defence witnesses — including Mrs Leifer herself — and argued their client did not commit any wrongdoing.

Defence barrister Ian Hill said the sisters, who suffered a traumatic upbringing, made up the allegations against the former principal and that their story "grew like wildfire".