The teacher at Porirua's Aotea College, Carey Adrian Straayer, is still listed on the college website as a teacher of English and social sciences. He has taught there since 2003.
The tribunal has censured him for deliberately accessing 17 websites on his school computer, including adult comic book sites, online gaming and fan-created artwork and other material.
He also used a photo of his girlfriend with her cleavage showing as the background image on his screen, and told the tribunal that this may have been the image of "boobs" that the students saw.
But the tribunal has allowed him to continue teaching on condition that he informs any employer in the next two years about the case.
"This conduct is at the lower end of the scale of seriousness," the tribunal said.
The tribunal's decision says the case came to light after a student told his parents about what he had seen in March 2018.
"The parent complained that their child had seen sexually explicit content on the respondent's computer during class, and this content included a picture of 'boobs' and a Facebook message reading, 'I have an open relationship with my husband – do you want to f---?'" the tribunal said.
"As a result of a technical investigation of the respondent's computer, it was established that there were 17 websites that the respondent accepts he deliberately accessed which included adult comic book sites, online gaming and fan-created artwork and other material. These sites were accessed outside of school hours.
"The laptop had attempted to access four pornographic websites, a total of 2214 times.
"It was explained that when an internet browser attempts to gain access to a website [whether deliberately or otherwise] it can attempt to do so again through cached data. This may be deliberate, or may be an attempt made by the computer itself due to the
compromised security of the device. Cached content is created when content from
websites that have been accessed is stored on the computer.
"The investigation found that inappropriate images were on the laptop. It was not able to establish whether the images were from websites that the respondent had deliberately visited, or were on the laptop because of its compromised security.
"In addition, photographs of the respondent's partner were stored on the laptop.
"It was further found that the browser history on the laptop had been deleted. The
laptop had not been set up to automatically delete the browser history when shutdown."
Straayer acknowledged that he had accessed the 17 websites containing adult material.
"He accepted that while using an online learning game during a lesson, a popup advertisement for an adult game site had been seen by students," the tribunal said.
"He stated that the image of 'boobs' referred to may have been a picture of his partner in which her cleavage was visible, which he had saved as a desktop background.
"The respondent accepted that in accessing appropriate comic book and gaming sites, he may have exposed his computer and the college system to a risk of being infected by pornographic material.
"He denied deliberately going to the pornographic websites but explained that the websites that he accepted going to contain a great deal of popups for other websites that were in the nature of the pornographic websites.
"The respondent confirmed that he was aware of the high-risk nature of the websites that he visited, and that they were in breach of college policy and exposed the students and school to risk.
"He acknowledged that in order to access one of the sites he deliberately visited, he had intentionally disabled the internet's ad blocker. The respondent maintained that he did not clear the internet browsing history from his computer.
"The respondent subsequently apologised to the college, agreed to future monitoring of his electronic devices and purchased his own laptop for personal use.
"He also participated in a restorative process with students affected by his actions. He accepted a final written warning from the college."
The tribunal found Straayer guilty of "serious misconduct" but said the misconduct was not as bad as some other cases where teachers had passed on pornographic images on their school emails or accessed "hard-core" porn during school hours.
It said Straayer's actions were "careless, reckless and reflected very poor judgment" and were "likely to adversely affect the wellbeing or learning" of his students.
"At worst, a student might be disturbed by what they had seen," it said. "At least, students must have been distracted, which might adversely affect their learning."
Meanwhile, the tribunal has also censured West Auckland teacher Kimberley Carlene Anne Kopp, aged 56, after she was convicted for a third drink-driving offence in Kumeū in 2017, after similar previous convictions in 2007 and 2009.
