A "brazen, predatory and opportunist" teacher caught filming up the skirts of schoolgirls has had his sentencing delayed as a doctor considers whether he has a disorder that could impact on jail time.

Eric Wong, 28, has pleaded guilty to two counts of filming a person's private parts without consent.

The teacher breached his position of authority and trust, preying on girls he taught, photographing and filming their pelvic and chest areas under their school uniforms in a "brazen, predatory and opportunist" way, agreed facts filed with the court state.

A 16-year-old student, asked to stay behind after class to complete a survey, bumped into a smartboard at Cammeraygal High School on Sydney's lower north shore and revealed a hidden phone strategically placed to film.

Wong immediately leant down to pick up the phone, said he left it there before class, and changed the topic when the girl questioned him.

She believed the phone was purposely placed there to film her while she completed the two-question survey on her teacher's laptop at his work bench.

No such survey had been authorised by the school or the education department, principal Kathy Melky told police after the student reported the incident to her friend, a parent and the school.

Wong was arrested and cautioned, declining legal advice and giving an electronically recorded interview before being released pending further investigation.

He gave another interview when he was arrested 10 days later, declining to answer the allegations.

Police found 90 videos and 300 photos of uniformed students, including images taken up skirts and down shirts when they searched his home.

The files were found on two computers, showing him "randomly walking around" his classroom with his phone camera recording, targeting only the girls.

He walks up next to or behind them, and while supervising their schoolwork, discreetly films their private parts under their school uniforms.

Some videos show him glancing towards the phone before repositioning it.

Wong was due to be sentenced in Hornsby Local Court on Wednesday, however his lawyer Peter Givorshner secured an adjournment for a report to be prepared.

"The report ... raises the possibility of an autistic spectrum disorder which we would say would be highly relevant to the court's approach to sentencing," the lawyer said.

Police prosecutors opposed the adjournment "primarily on the basis of the ongoing distress these matters are causing to the cohort and the community of the relevant high school".

Magistrate Alexander Mijovich said he understood the opposition but the defence was entitled to put material before the court and had not caused any delays before.

"It's not a matter I foresaw being adjourned but on the material before me it is appropriate," he said.

"There won't be any further adjournments, if material is not ready it's not ready."

Wong is living with his parents as a condition of bail and will return to court on July 19.

National Sexual Abuse and Redress Support Service 1800 211 028

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