I don’t want a support person. I demand a representative

Whenever a meeting with management has the potential to have disciplinary consequences, it is essential that members do not go in alone. Enterprise Agreements will generally codify this, but natural justice would determine this right anyway.
If your letter of meeting notification talks of bringing a support person, this should be challenged (ahead of the meeting if possible) because a “support person” is not entitled to speak on your behalf at the meeting. They are merely there to provide emotional support and take notes.
A representative, however, may take an advocacy role if and when necessary and may call for breaks or even the postponement of the meeting in extreme circumstances.
Who can be your representative? A trusted colleague may be able to perform the role, but generally people do not understand the role and if that colleague is a line manager they will have a serious conflict being a representative of management needing perhaps to take a strong stand against management in your defence.
Some workplace Union Reps have had training in their representational role, but generally members should contact the school’s Organiser for advice. If the Organiser is to come in as your “Representative” the meeting may need to be rescheduled to accommodate their availability.
Some schools try to avoid the formal notification and representative issue by setting up an ambush meeting, (often Friday afternoon) with an innocuous “would you mind popping by my office before you go today?”
All such requests should be followed with a request for the purpose of the meeting. If that purpose is potentially serious, request that the meeting be formally notified in writing. If the meeting is initially about a minor administrative arrangement and turns with “while I have you here there is another thing I would like to discuss”, then it may be time to bail on the meeting and get it formally rescheduled.
Procedural fairness is your right and serious meetings require detailed allegations prior to the meeting and time to prepare responses.