Teachers in independent schools have bucked the national trend and rejected strike action over pensions reform.
A separate ballot for the sector, run by the Scottish Secondary Teachers' Association, showed that a narrow majority did not want to strike over pensions.
The union had initially decided not to consult teachers in independents, fearing they did not have the same employment protection.
But many teachers at the schools later indicated that they wanted to be balloted.
John Edward, director of the Scottish Council of Independent Schools, said the SSTA ballot was the "final piece of the jigsaw" as independents sought to clarify how they would be affected by strike action. There had been no talk of closures as TESS went to press, although that had not been ruled out.
But Scottish teachers in the state sector are heading for their first national strike since the 1980s, after two more unions voted in favour of action over pensions.
The SSTA and the Scottish branch of the NASUWT will join the UK-wide action by public-sector unions on November 30.
Four out of five SSTA voters wanted to strike, based on a 66.3 per cent turnout of those canvassed. NASUWT members voted "overwhelmingly" for action, said Scotland organiser Jane Peckham, but she was unable to provide actual figures.
The secondary heads' body, School Leaders Scotland, is now the only Scottish teachers' association or union not to have balloted its members on strike action.
General secretary Ken Cunningham said members were "as unhappy around pensions as other people", but ongoing talks with the Government, involving SLS and the English school leaders' body to which it has links, ASCL, meant a ballot was not appropriate.
Cabinet Office Minister Francis Maude has threatened to withdraw a revised deal the Government put on the table this month if workers go on strike, prompting teaching unions' outrage.
"I think that can fairly be seen as an attempt to blackmail the unions," said EIS assistant secretary Drew Morrice.
Mr Maude's stance did not make sense, he said, as the detail of the offer had still to be teased out; no one knew exactly what was on the table.
SSTA general secretary Ann Ballinger said Mr Maude's attitude was "obscene". She contrasted his pension pot - said to be #163;43,000 a year - with teachers' typical post-retirement income of less than #163;9,000.
Meanwhile, the general secretary of education directors' body ADES, John Stodter, told TESS that the decision to close a school would be made by the education director, along with the corporate management team and the headteacher. It was not like winter weather closures, for which the head's advice is typically the deciding factor.
Results in the latest union ballots
SSTA - 79 per cent of voters in favour, based on 66 per cent turnout. The union represents 9,000 teachers, but could not provide figures on actual voter numbers, explaining that it was policy to give percentages only. The ballot did not involve members who were retired, on supply, or whose employment status was unknown.
NASUWT - A decisive vote in favour but no Scottish figures provided on either turnout or number of votes. Information on voter numbers in England, Wales and Northern Ireland was published on the union's website. TESS made repeated requests for Scottish figures, but was told they were not available.