Heads would be vital to any restructuring plans but this week both the Association of Head Teachers in Scotland and the Headteachers' Association of Scotland rejected a deal.
Nigel Lawrie, HAS president and head of Port Glasgow High, said the plans would sweep away the existing management and organisation of secondaries without imposing any specific or detailed structure.
In a letter to Sam Galbraith, the Children and Education Minister, and Danny McCafferty, the local authorities' chief negotiator, Dr Lawrie states: "The lack of structural models to accompany the offer is not reassuring and there is little in the proposals dealing with the strategic management of schools and the role of senior managers."
He adds: "As they stand, the proposals imply a greater workload for senior managers, accompanied by a very modest increase in salaries over a three-year period. We remain unconvinced that the role envisaged for professional leaders can cover the tasks currently being undertaken by middle management and will consequently make it harder to drive forward curricular changes such as Higher Still."
Dr Lawrie says the loss of thousands of promoted secondary posts is bound to lead to hit morale. Salary increases will not compensate for the loss of status.
The HAS, which represents secondary heads, deputes and assistants, believes its voice could help break the negotiating deadlock. Along with other unions and associations it has been squeezed out of talks between the local authorities and the Educational Institute of Scotland, the lead union.
Bill Milligan, president of the AHTS and head of Dalmilling primary, Ayr, described the offer as "derisory" over three years. Major changes to conditions of service would place extra burdens on heads "with not the slightest reference to parity of salary".
Primary heads are currently demanding equality with secondary colleagues and have launched a test case through an employment tribunal in Glasgow.
Mr Milligan said the mood of staff was "sombre". They were not rejoicing at the offer and were uncharacteristically silent.
Meanwhile, ballot papers are being sent to 45,000 EIS members following the rejection of the offer by the union's executive council with the result due to be announced in around two weeks.
Ronnie Smith, the union's general secretary, said the offer was "wholly unacceptable and would be damaging to schools and pupils". The employers were seeking to raise composite class sizes and extend teachers' duties in return for average pay rises.