Does a meeting of the superintendent, chair and vice-chair to set the agenda have to be posted as a committee meeting?
As long as the chair and vice chair are not meeting as a committee to discuss and deliberate on district business that is under the board's jurisdiction and bring a recommendation to the board, it is not a meeting that must be posted. Agenda-setting falls under the category of "housekeeping topics," not a recommendation to the board on district business. Ultimately, the full board decides on the agenda when it is brought to a board meeting. Other things your small group can discuss include dates and times of meetings, room arrangements and other procedural decisions.
If you added the third member of a five-member board to the group or the fourth of a seven-member board, I would recommend posting the meeting, because there would be a quorum present, although the argument could still be made that they are not deciding policy or administration issues. As long as less than a quorum is present, there should be no need to post the agenda-setting session as a committee or board meeting. As the Attorney General's Public Records and Meetings Manual states: "A gathering of less than a quorum of a committee, subcommittee or advisory group or other governing body is not a 'meeting' under the Public Meetings Law."