Toon, who taught maths at the school since 2001, was found guilty last month of committing an indecent act in an empty classroom at the school during lunchtime in June 2013.
His teaching certificate is under interim suspension and he is not currently teaching, stepping down when the incident was disclosed.
Toon had denied masturbating but had conceded watching pornography. His lawyer accused the schoolboy witness of "making up a story for his mates".
Judge Anne Kiernan sentenced him to nine months supervision, with counselling or treatment as appropriate and 80 hours community work. She lifted suppression, but Toon appealed.
Toon's alleged sexual history has been previously documented, beginning with his police interview during a rape investigation in 1991.
The woman who made allegations against Toon had what a doctor described as "multiple injuries to the face, nose, jaw,neck and teeth", the Sunday Star-Times reported.
Toon told police they had had consensual sex and the woman was fine when he left her in a Parnell alleyway. Police concluded there was insufficient evidence to bring charges.
Toon, who was teaching at Auckland Grammar at the time, went on to teach at King's College, also in Auckland.
While there, he was subject to an employment dispute in which he admitted downloading pornography on another teacher's computer but denied a claim by a female colleague that he waged a two-year sexual harassment campaign against her.
The woman took a case to the Human Rights Review Tribunal alleging Toon had breached the Human Rights Act's harassment provisions.
The case was abandoned four years later due to the complainant's ill health. Toon was awarded $10,000 legal costs. His lawyer said it was "grossly unfair" the claims were made public and his client was denied the chance to put his side of the story.
Toon left Kings in November 2000 after reaching a confidential agreement with the college.
After his departure, King's College told the Teachers' Council Toon left at the commencement of a disciplinary process about his behaviour and computer use but did not mention the allegations involved pornography and sexual harassment.
It refused to provide the council with further details, citing privacy law.
Toon was then re-hired in January 2001 by Auckland Grammar, which was not aware of the King's College issues - and didn't look into it further after being alerted by media.
When questioned by the Herald in 2003 about the re-employment of Toon, headmaster John Morris said Grammar had followed normal procedures and Toon was "well-known as a top-class teacher and a very good colleague".
"He's been an exemplary employee. The key point is that all this happened elsewhere, not with us. These events had nothing to do with us."
Mr Morris retired as headmaster of Grammar in 2012 but went on to lead the transition of the Teachers Council into the Education Council of Aotearoa New Zealand, as the new professional body for teachers responsible for disciplinary matters.
At the time, Section 139 of the Education Act required schools to provide the council with a description of the conduct being investigated.
Teachers' Council head Peter Lind said at the time that steps had since been taken aimed at requiring schools to report the details of serious allegations to the Teachers Council. It had previously admitted that any instance where a school came to a private agreement with a teacher was a problem.
The Council would wait until criminal processes were complete to continue with its investigation into the latest matters.
Auckland Grammar School said in dealing with the 2013 complaint against Toon, it had acted quickly and in the best interests of students and staff.
Board of Trustees chair Jeff Blackburn said the student and staff welfare was of paramount importance.
"We set very high standards of behaviour for our staff and it's what our community expects. It is a rare and serious event when we have to act to uphold those standards, but we did so swiftly and thoroughly," Mr Blackburn said.
He said Toon was suspended following the complained and then resigned partway through a formal disciplinary process, without returning to the classroom.
The school informed the Teachers' Council straight away.
Simon Toon was employed by the School between 1986-1993 and again from 2001-2013.
Timeline of events
1991: Toon, a teacher at Auckland Grammar, is questioned by police investigating a rape complaint. Police conclude there is insufficient evidence to press charges.
2000: Toon is now teaching maths at King's College. He leaves in November after reaching a confidential settlement with the school. He admits downloading pornography on another teacher's computer but denies a claim by a female colleague that he waged a two-year sexual harassment campaign against her. The woman takes a case to the Human Rights Review Tribunal.
2001: Toon is hired in January by Auckland Grammar, which is not aware of the reasons Toon resigned from King's as the school did not tell the Teacher's Council the reason for his resignation.
2003: The Herald reveals details of the confidential settlement and tells Auckland Grammar. Principal John Morris expresses confidence in Toon.
2004: The complainant in the Human Rights Review Tribunal case drops the allegations due to ill health. Toon was awarded $10,000 legal costs.
2013: Toon is seen masturbating at school in an empty classroom while watching pornography. The school investigates, he resigns, and the matter is taken to the Teachers' Council, who pass it on to police.
2015: Toon is found guilty of of committing an indecent act in an empty classroom at the school during lunchtime. He appeals for name suppression, and is denied.
