Ratu was charged with assault over that incident. He pleaded guilty and was discharged without conviction in 2019. He also attended a Man-Up programme, wrote an apology letter and paid $300 in emotional harm reparation.
In its November 10 decision, the tribunal said Ratu had argued he was stricter with Student B because he was "one of his mokos".
But the tribunal said the fact a student is related to a teacher does not lower the expectations of the teacher's behaviour.
Ratu had already lost his job in October 2018 after the Teaching Council asked him to sign a voluntary undertaking not to teach while the complaints were being investigated.
But Tokoroa High School later offered Ratu a job, and the council let him take up the offer with some conditions.
However, it reversed that decision in September 2019 after two further incidents: one in which he pushed a 15-year-old and grabbed his arm after a dispute over incorrect uniform, and a second in which he drove a female Year 10 student to a speech
competition after having been denied permission to do so by the school.
The disciplinary tribunal found most of the incidents constituted serious misconduct.
It cancelled his registration, saying that was appropriate given how many incidents there had been, as well as Ratu's continued use of inappropriate force after being discharged without conviction in the assault case.
Ratu had filed a 12,000 word document titled "My Life, My Journey", which detailed a rich, loving upbringing and talked about religious teachings, but dwelled very little on the events in question.
"There was nothing in the respondent's document that mitigated the conduct or his current situation. There was no expression of remorse or any indication that he would do anything differently in the future," the tribunal said.
"The extent of his wrongdoing along with his lack of insight into his behaviour raise serious concerns about his fitness to be a teacher.
"He has assaulted children, undermined his colleagues and shown no evidence of rehabilitation in the form of meaningful reflection on his aberrant behaviour, professional development, or engagement with colleagues or mentors.
Ratu's practising certificate was due to expire on May 29, 2021.