The association's annual meeting in Glasgow last Saturday threatened to degenerate into name-calling after Mr Fairweather was nominated for the presidency, despite Mrs Vass having been named by the executive board - which includes Mr Fairweather - as president-elect and sole nominee for the post at the beginning of the month.
Annette Mitchell, representing Shetland, intervened at one point, shouting:
"This is an organised plot - it smells."
Mr Fairweather's nominator, Kenneth Low, also from East Dunbartonshire, criticised Mrs Vass's style of leadership and communication problems.
Mrs Vass won the vote by 23 votes to nine, but only after members had debated a variety of motions, including the possibility of holding a postal ballot and an extraordinary general meeting to allow them to postpone choosing between the two candidates.
However, such options were ruled unconstitutional and a straight vote was held, despite a number of new board members declaring themselves unable to choose between the candidates.
At the heart of the split appear to be moves led by Mrs Vass and George Hammersly, the SSBA secretary, but endorsed by the executive board, to seek a rapprochement with the Scottish Parent Teacher Council and create something of a united front against proposals from the Scottish Consumer Council to set up a new single parent body once the Parental Involvement Bill becomes law.
Last year Mrs Vass emerged as president after the executive board turned against the more consensual style of Alan Smith, her predecessor. Now she, in turn, has been challenged by hardliners who appear to be fighting for the SSBA to be turned into the sole parent body under the new legislation.
Mr Low, proposing Mr Fairweather as the new president, said the association had "lost touch with school boards at the grassroots. I don't feel we are being listened to."
In her "acceptance" speech, Mrs Vass warned: "The SSBA has the potential to tear itself apart - there is nothing new there. For the six years I have been here, it has always been the same - desperately trying to make sure that democracy rules. It is very difficult when decisions are taken by the board and then people speak against that."
Turning to Mr Fairweather, she said: "As vice-president, you have come to one meeting of the board. I would like a vice-president to give me more support than that."
Jim Manson, who for the past 13 years has advised the SSBA on transport and for the past three on personnel, has resigned his position over differences with Mrs Vass. He cited the "lack of professionalism by some members of the executive board, especially at a time of crisis".
Mr Manson said that if Mr Fairweather had been elected president he would have stayed on.
Earlier in the proceedings, Mrs Vass told the meeting: "The SSBA board was quite concerned about hearing of proposals for a new national body (for parents). We are the national body for parents through school boards.
"The SPTC is also concerned because it is the national body for parents through PTAs. We were concerned about inactivity and, as someone who has served on school boards and PTAs, I was concerned about school boards and PTAs."
Mrs Vass said that the SSBA board had approved discussions with the SPTC and both agreed that "PTAs, boards or whatever we end up with should be represented by the people who are leading them now".
Meanwhile, in another twist, it is understood that Jennifer Gallacher, the Dumfries-based SSBA office manager who is the organisation's sole employee, has taken out a grievance against Mrs Vass over their working relationship.
Rumours of a proposal to rent office space from the SPTC in Edinburgh are said to have been another bone of contention between the two.