A former teacher from an Auckland school has been found to have been masturbating in a classroom while watching pornography.

However he is yet to be found formally guilty as he disputes the classroom was a public place.

The man, in his late forties, was on trial at the Auckland District Court charged with committing an indecent act in a place the public have access to in June 2013.

He denied masturbating but had conceded watching pornography in an empty classroom at lunchtime.

The incident came to light after a student wanting to speak to him about a timetable change viewed him through a window, after a friend lifted him up to look inside the classroom.

The teacher's name, plus that of the school, remains suppressed until a further hearing.

His teaching certificate is under interim suspension and he is no longer working. The school does not support the continued suppression.

Sitting before Judge Anne Kiernan, who heard the case alone last week, the court heard how the boy, now aged 17, had liked and respected the teacher prior to the incident.

Afterwards, he was left shocked and "never wanted to speak of it again", a friend said.

The boy gave evidence sitting just metres from the man. He was grilled extensively on the details by defence lawyer Richard Earwaker, who accused him of "making up a story for his mates".

However the judge found the boy was a truthful witness.

Others to give evidence included the school principal, a teacher, a teacher aide, an IT expert and police.

The school's head of IT said a server log showed that the teacher had been accessing Tumblr sites with various URLs.

The defence disputes the allegation that the act took place in public and has indicated that it will argue that the teacher had a reasonable expectation of privacy at a further hearing.

This is despite a previous ruling saying it could have been considered a public place.

The man will reappear on May 22.