Mr Haggarty will warn the association's annual conference today (Friday) of severe inequities in school funding. The headteacher of St John's High, Dundee, points out that at least 13 of Scotland's 32 authorities claim to be underfunded in respect of implementing the teachers' national agreement and predicts a further financial squeeze as pressures grow on the Scottish Executive.
"At the level of our members, this means that the quantity and quality of support for headteachers and schools can vary considerably from one authority to another," he says. "Likewise, some authorities have been able to use resources to develop more creative flexibility at headteacher and school level while others have been constrained from doing so."
Mr Haggarty calls for more collaboration between councils, a refrain that will be received warmly in the Executive which is keen to modernise local government and seek inter-authority agreements.
He says: "We need a more sensible and equitable solution to the funding of local authorities and we need to see more collaboration between neighbouring authorities to produce more strategic solutions to issues such as teacher and supply teacher availability, the provision of leadership and CPD programmes, and the developing and sharing of quality curriculum resources."
Lindsay Roy, head of Inverkeithing High, Fife, who is the outgoing president, says that heavy investment in leadership training will not by itself produce the anticipated gains when there were still major issues around the amounts of targeted funding that actually reach schools, new management structures and job-sizing.
Those were reasons why heads and deputes in secondaries continue to spend 70 per cent of their time reacting to the daily events and not on "proactive, leadership and management tasks".
Despite considerable investment in support staff promised under the agreement, some had not reached schools. "Why is it that senior staff are still undertaking some basic and routine administrative functions? Why is it that support staff are not in place to allow a brief morning break or more than a few minutes at lunchtime?" Mr Roy asks.
Both heads say their criticism is offered as constructive comment in a new partnership with the Executive and local authorities.
Mr Roy commented: "We have endorsed the stance taken by Peter Peacock to retain Scottish state education within a framework of local democracy - and his commitment to ensure effective support to schools that are not performing well - rather than adopting what appears to be the preferred model in England of closing such schools and seeking alternative providers."
There was a clear Scottish consensus on the overall principles, direction and objectives of education. It was a "shared agenda".
Mr Haggarty commends key aspects of the national agreement but questions the extent of collegiality in schools. "We still need to promote awareness among staff of the renewed and reinvigorated professional culture to which the agreement was directed. Have we at times lost sight of this?" he asks.