A former boarding school teacher accused of grooming a child on a dating app was not sure he was messaging with a real person, his lawyer says.

William Roberto Gulson taught at Knox Grammar School in Sydney’s north before he was charged over his messaging with a 15-year-old girl, posing as a boy, in August 2024.

The 28-year-old faced a contested hearing today after pleading not guilty to procuring a child under 16 for unlawful sexual activity.

The 15-year-old and another teenager were running a fake profile on the LGBTQI dating app Grindr to catch pedophiles, a prosecutor told the Downing Centre Local Court.

Their account was under a pseudonym and was being operated by the girl when Gulson began sending messages.

Though the fake profile presented as a 15-year-old boy in year nine, Gulson said he was keen on meeting and interested in “kissing, sucking, f—ing and cuddling”.

The defence did not dispute the messages.

However, Gulson’s lawyer pointed out that Grindr is restricted to adults, and the former drama teacher had not believed he was talking to a child.

“He wasn’t even sure that he was dealing with a real person,” lawyer Paul Glissan told the court.

“The text messages indicate his scepticism over whether he’s dealing with a real person or a robot.”

“His intention was never to have unlawful sexual activity with anybody – whether that be a real person or a fictitious person.”

After requesting photos from the account, Gulson received an explicit image that appeared to be of an adult man, Glissan said.

Gulson eventually asked if he could pick up the person he believed he was talking to and offered to find a meeting place.

At that point, the 15-year-old ended the conversation and deleted the fake profile, the prosecution said.

It is not alleged that any sexual activity took place.

Gulson has been on bail since being charged a year ago.

Knox Grammar, on Sydney’s upper north shore, is among Australia’s most elite schools, charging annual fees of up to $43,170 per student.

Boarding sets families back another $39,210 per student.

For under 25s: Kids Helpline 1800 55 1800.