The unprecedented legal test case that primary heads hope will bring them pay parity with secondary colleagues will be launched before the end of the summer term, the Association of Head Teachers in Scotland (AHTS) confirmed at its conference in Dunblane last week.
All 1,500 members, including deputies, are being asked to submit claims against their employers for higher pay under the Equal Pay Act. They will claim sex discrimination - primary teachers are more likely to be women - and equal pay for like work or work of equal value.
Should they win, they would add 1 per cent, around pound;11 million, to the pay bill.
Three primary heads will contrast their salaries with secondary heads of similar-sized schools. Heads of large primaries earn about pound;4,000 less than those of small secondaries.
Rena Mitchell, AHTS president and head of Forth primary, South Lanarkshire, rejected pleas from Elizabeth Maginnis, the employers' chief negotiator, to reach an agreement through collective bargaining. She said: "This cannot be done by negotiation. We've tried to negotiate this for the past eight years and failed. We've been extremely patient."
Bill Milligan, salaries convener and head of Dalmilling primary, South Ayrshire, said: "Primary heads do similar work or if not, work of equal value to secondary colleagues and there's a prima facie case of sexual discrimination. We're going to challenge that."
The case was delayed for several months while the association took last minute legal advice.
Mrs Mitchell said equal pay was already established on all posts up to senior teacher. Primary heads are already on the same pay scale, but on a different banding. They have the same conditions and job descriptions.
The association accepts new money would be needed to finance any regrading of the senior posts in primary. It wants all heads, deputies and assistant heads to be pushed up the pay scale and pupil numbers to determine pay levels.
Maire Whitehead, head of St Mirin's primary in Glasgow and AHTS vice-president, said equal pay would reflect the emphasis by the Government and the profession on early intervention and ensuring children got the basics right in primary.
"This would increase the morale in primary schools. Everyone says the primary school is of prime importance and one way of recognising this is paying salaries that are appropriate," she said.
The authorities are certain to contest the claim, even if they have to justify discrimination. They are likely to argue they have been restricted by legally binding national agreements.