Primary heads and deputes have demanded evidence to support the benefits of shared headships, after a TESS survey revealed a dramatic surge in the past decade.
Greg Dempster, general secretary of the Association of Headteachers and Deputes in Scotland, said: "This is coming about not through an analysis that tells us shared headships are good for schools but by the back door, because some local authorities are having trouble recruiting headteachers - or they are looking to save money."
He questioned whether shared headships were in the best interest of pupils. "I would need to see a lot more information before I was convinced you'd get a better quality of education," Mr Dempster added.
Ronnie Smith, general secretary of Scotland's largest teaching union, the Educational Institute of Scotland, was equally sceptical about the practice of making one headteacher responsible for two or more schools.
He warned the trend was likely to grow as councils looked to save money and, like Mr Dempster, demanded more evidence of its effectiveness. Shared headships were "discriminatory against rural schools", Mr Smith argued. "What they are saying is: you are second-class; you are not entitled to a headteacher; you are a burden," he said.
The union chief's comments are likely to rankle with Education Secretary Michael Russell who last week upped the pressure on councils to devise alternatives to closing rural schools, potentially paving the way for an even greater number of shared headships.
The TESS survey of Scotland's 32 local authorities revealed that 113 headteachers had responsibility for two or more schools in 17 councils, ranging from 33 shared headships in Highland and 21 in the Borders to just one in both North Ayrshire and Argyll and Bute.
The remaining 15 councils had none at all and tended to be the less rural authorities - Edinburgh, Glasgow, Aberdeen and Dundee.
However, there was some evidence from the survey that shared headships were creeping into more populated areas. North Lanarkshire Council agreed a policy last year and currently has two shared headships involving schools in Airdrie, which has a population of 36,000.
East Lothian is on the point of hiring its first headteacher with responsibility for two schools and estimates shared headships would save it between pound;17,000 and pound;24,000 per pairing. This made small rural primaries more affordable and was an alternative to closure, it claimed.
North Ayrshire's one shared headship on Arran saved the authority around pound;55,000 per annum; North Lanarkshire estimated it reduced costs by pound;15,000 per pairing; and South Lanarkshire was better off to the tune of pound;304,000 per year through eight shared headships, roughly pound;38,000 per school.
However, the majority of councils were adamant that introducing shared headships was not about money.
Aberdeenshire Council, which has nine shared headships, claimed they could cost thousands more than individual headships. This was because they were paid higher salaries, the authority put in a principal teacher in each school and additional teachers were appointed so the head could concentrate on managing the school.
The change had been introduced, the council stated, because it was becoming harder for class-committed headteachers to balance teaching with leadership and management duties which had increased significantly over the past decade.
Aberdeenshire had experienced a "clear reduction" in the number of applicants for headteacher posts in smaller schools. In addition, a large number of heads were due to retire; the introduction of chartered teachers meant teaching heads no longer earned significantly more; and the repeal of the 1956 Schools Code removed the requirement that there be one head for every school.
West Lothian Council also maintained its six shared headships were not put in place for financial reasons but to reduce the number of teaching headships and to solve recruitment problems.
A spokeswoman said: "For small schools with a teaching headteacher, we had to repeatedly advertise headteacher posts - in one case six times."
But Mr Smith of the EIS remained convinced that there was "one single motive" for shared headships: "to save on costs".
Mr Dempster suggested that if local authorities wanted to recruit and retain more headteachers, they should adopt the recommendations contained in Scottish Government research published last year. These included reviewing the salaries of heads and deputes; reconfiguring the scope and the nature of responsibilities devolved to schools; and treating heads as "senior partners rather than middle managers".
SMALL BUT MIGHTY
Baltasound Junior High, situated on the island of Unst in Shetland, is the most northerly school in the UK. Its depute head, Maggi Reyner, is responsible for the primary department and Fetlar Primary, a 25-minute boat ride away on the island of Fetlar which, according to the 2001 census, had a population of just 86.
Currently two children attend Fetlar Primary's nursery; next year, there will be one pupil in P1 and Ms Reyner will make the journey to the island once a week to support the school's teacher.
Of the 113 shared headships in Scotland, revealed in The TESS survey, three are in Shetland with a fourth soon to be established following the controversial reopening of Papa Stour Primary. The school has been billed by the tabloid press as "the most expensive school in Scotland". It will have one pupil and cost pound;56,000 a year to run.
Just three local authorities - Dumfries and Galloway, the Borders and the Western Isles - had shared headships involving more than two schools, The TESS survey found.
One of the most unusual was the partnership of Dalry School in Dumfries and Galloway, which takes pupils up to the age of 16, Carsphairn Primary and Kells Primary - a combined population of about 200 pupils.
North Ayrshire Council, meanwhile, recently agreed heads of schools with fewer than 100 pupils could be made responsible for a maximum of three schools. The authority brought in the new rules after scrapping plans to place the seven primary schools on Arran under the control of just two headteachers, following objections from parents.
Perth and Kinross has a shared headship with a difference. The authority has two conventional shared headships, but at Comrie Primary two heads share responsibility for managing one school.
The arrangement was put in place when the headteacher requested flexible working hours after returning from maternity leave. A report on the progress of this pilot is due next month.