The ASTI has been accused of many things - not all of them justified - during its troubled pay campaign. But this morning the union is vulnerable to the most damning charge: that of misreading the mood of a significant minority of its own membership.
One senior school manager - Mr Michael Moriarty, of the Irish Vocational Education Association - reflected this view. The result of the ballot, he said, placed a question mark over any future industrial action by ASTI. "Their standing committee clearly misjudged the mood of the membership."
The relatively tight margin on the Labour Court vote and the overwhelming opposition to the ban on exam work, is a disappointment for the hardliners within the ASTI, who have driven the union's agenda for the past 18 months.
It was this group who ensured that the ballot was delayed until shortly after the annual conference. Their hope was that the strong opposition of the conference to the Labour Court offer would boost the No vote.
The Galway conference voted three-to-one against the court offer. However, on the basis of last night's result, it is clear the 500 delegates took a stronger line than the general membership of 17,000. The conference did not fully reflect the mood of the wider membership.
The tactic of delaying the vote until after the conference also backfired. While the conference underlined the real anger about the Labour Court offer, it also generated a good deal of negative publicity. The alleged verbal and physical assaults on members of the National Parents' Council may have driven a lot of potential No voters into the Yes camp.
The ASTI members who voted Yes to the Labour Court offer may have done so for other reasons. The promise of £1,750 for making up lost hours to exam students concentrated many minds.
One hardline executive member suggested another reason: "It was not that we lost the argument on benchmarking. It is just that many teachers who might be opposed to it have no great confidence in this union to mount a successful campaign."
For all that, a decisive majority of members rejected the Labour Court offer. A majority has said No to the benchmarking pay review. A majority appears ready to fight on. That, in itself, underscores the sense of anger and frustration, the real crisis of morale among many secondary teachers.
The result probably lessens ASTI's room for manoeuvre. Its membership will be balloted later this month on a range of possible options designed to give some new vigour to the campaign. These include:
A ban on all voluntary work, including supervision and substitution duties;
Withdrawal from all co-operation with Department of Education initiatives;
A ban on all extra-curricular activities such as sport, drama and debates.
The most contentious of these is the proposed ban on supervision, which could lead to closure of schools. This is what happened late last year when ASTI withdrew from supervision for five days.
But the situation may be very different in September. For one thing, school managers have received advance notice of ASTI's plans and seem determined to avoid closures, even if this means employing non-teaching staff to supervise.
More importantly, the Department of Education and the other teaching unions are working on new arrangements for paid supervision. The Department, the INTO and the TUI will meet next Tuesday to work out a new hourly rate for supervision duties. The ASTI is refusing to participate until its pay claim is settled.
But what will happen if a new paid system for supervision is in place for the other teaching unions by September? Can the ASTI withdraw from supervision with credibility when money is on the table? Moreover, are members ready to support a withdrawal from supervision in a ballot this month? Next Wednesday's meeting of the 180-member central executive council is expected to be an angry and bitter affair.