The trespass order came after two separate meetings in which Fitchett placed a dictaphone on the table in protest against a resolution passed by the board that audio recordings could not be made at the meetings.
He said the batteries were not in the device on the first occasion.
He did the same thing at the next meeting, but refused to answer when the board chair asked him several times whether the device was turned off.
The next week, Fitchett was served with a trespass order banning him from school buildings for the next two years, but he has challenged the order in court.
"The chairman had taken the view that the applicant's behaviour 'was likely to prejudice or continue to prejudice the orderly conduct of the meeting if [Fitchett] remained',"said the earlier judgment.
His lawyer, Luke Acland argued this morning it was "unlawful" to issue a trespass order when Fitchett had a right under the Local Government and Official Information and Meetings Act (LGOIMA) to attend the meetings.
He said the matter should be dealt with in each separate meeting, if Fitchett was being disruptive at that time.
Acland, who is also a member of the Nelson City Council, said he could not prohibit someone from attending council meetings if he did not like the things someone was saying about him.
Fitchett had also sent letters to three former board members focusing on the Fitchett brothers' view that a resolution appointing a subcommittee to inquire into a disciplinary issue regarding two volunteer basketball coaches had been fabricated by the principal.
The letter said the board members' replies would be "a test of your ethics and moral standards.
"I close by noting my belief that, although the headmaster continues to attempt to hide it: the truth will come out: the sole questions are: when and 'how' will the truth affect people other than the headmaster," John Fitchett wrote in the letters.
The recipients made statements saying the letters were threatening and harassing.
In today's hearing, Justice Thomas questioned whether it was relevant that those letters and Fitchett's other behaviour made the board members feel "constrained" and the meetings were "impinged" by his actions.
Since Fitchett had been trespassed, Acland said his son had also been excluded from the meetings "because he was seen as an extension of Mr Fitchett".
David said what happened at the meetings "can't be trivialised".
"In the context of a school board running its meeting, that's disruptive conduct."
He said there was nothing in the LGOIMA "that says this is an overrule code".
"The context is everything here," he said.
Board members were giving up their time to help the school and it was "very important" they be able to control their meetings.
Board member David Rolleston gave a statement saying Fitchett's conduct has become "more and more disruptive over time" and eventually he became "confrontational".
He said the conduct meant the board had been unable to deal with its core business effectively and expediently.
In the earlier judgment, Justice Williams found Fitchett's behaviour "provocative and disorderly" and "frankly, extraordinarily immature for a man of the applicant's standing, age, and profession".
Justice Thomas reserved her decision.
