Local authorities, publicly, are backing the drive, described by Ewan Aitken, their education spokesman, as "a massive cultural change".
A new circular will spell out the precise areas they will have to devolve to secondaries and areas they will retain centrally. Heads have long complained that they do not know where headquarters money goes and fear it is siphoned off into non-critical areas, away from the classroom.
But the new benchmark is already being overtaken by South Ayrshire, East Ayrshire and East Renfrewshire, according to estimates for 2004-05 from Cipfa, the public finance and accounting agency. At the other end, Clackmannanshire and Fife prop up the table at just over 50 per cent. The Scottish average is 68 per cent.
Peter Peacock, Education Minister, last week addressed the annual conference of the Headteachers' Association of Scotland, and received a ringing endorsement of his revised devolved management plans.
"We want to see you in control of detailed staffing in schools with the local authorities facilitating your decisions, not determining your decisions. Local authorities' role should be seen as challenging and supporting the quality of provision but operating more in a supporting and enabling role," Mr Peacock said.
Heads would be given three-year budgets with most matters in their hands.
Lindsay Roy, outgoing HAS president, said heads did not want to go down the opting-out road but preferred "enhanced leadership capacity". "There is value in being in a local authority," Mr Roy said.
He added, however: "We have had reports that some of the funding to support Time for Teaching for additional support staff to free up management time has not been released by some authorities to the extent we believe Government intended it to be.
"Plus, there is good evidence that on occasion, when central government money comes in, local government money is withdrawn. For example, you get central government funding for two new classroom auxiliaries, but then local authorities withdraw funding for two classroom assistants."
He believed that at least one authority was cutting back its staffing formula despite the new maximum contact time of 22.5 hours a week. "We have heard that some local authorities won't be in a position to devolve all of that bit because of the financial stringencies within the authorities," Mr Roy said.
But Mr Aitken said: "Councils remain committed to delivering on 90 per cent. Some authorities will find it a hard task but it's the right thing to do."
John Dunford, general secretary of the Secondary Heads' Association south of the border, said: "We are much farther down the road of delegation than Scotland and English headteachers have always welcomed not only the financial freedom but managerial freedom to focus the money on the school's own priorities and make its own staff appointments."
Heads had control for the past 15 years and the percentage of delegated budgets had risen to over 90 per cent. Dr Dunford said primary schools had always referred more to the local authority.
Roy Jobson, president of the Association of Directors of Education in Scotland, said that there was nothing wrong with the principle of delegation but aspects such as funding school meals and transport should always be local authority matters. Delegation had to be targeted to improve attainment and should not place an extra burden on heads.
Mr Jobson, who was previously director in Manchester, said: "In England, many heads fell into the trap of being business managers."