survey said that they were having problems recruiting supply teachers, up from 23 last year. Fifteen local authorities said they had fewer primary teachers on their supply registers than last year and 14 reported having registered fewer secondary supply teachers.
A spokesman for North Ayrshire Council said: "It is becoming increasingly difficult to recruit supply teachers. This may be caused by many supply staff registering with a number of local authorities. In addition, recruitment for certain subject areas can be particularly low."
Midlothian Council also confirmed that it was struggling to find supply teachers, despite an ongoing campaign to increase numbers. A spokesman said: "Often, by the time we interview, candidates have been successful in gaining posts elsewhere."
A spokesperson for Stirling Council agreed. "It remains a challenge to recruit both short- and long-term supply staff," they said. "This year, we have taken the additional step of recruiting permanent supply teachers in order to build up a bank of permanent staff. Initial signs are that this is proving very helpful."
Perth and Kinross Council reported particular problems recruiting supply staff for primary schools and certain subjects in secondary, including English and science.
John Stodter, general secretary of school leaders' association ADES, said that recruitment problems had been made worse by councils "struggling to fill substantive posts in many parts of Scotland".
He added that numbers were affected by factors including the economy and the age at which teachers were able to retire.
Larry Flanagan, general secretary of the EIS teaching union, said the lack of supply was an issue across Scotland, but was "particularly acute in some subject areas and in certain areas of the country".
He added: "This lack of supply cover increases the workload pressure on teachers when colleagues are ill and can have a negative impact on the learning experience of pupils."
Budget cuts had led many councils to abandon successful systems of permanent supply pools, which had "exacerbated" the problem, he said.
Supply teachers' pay has been a contentious issue since a deal in 2011 tied them to a significantly lower daily rate unless they worked for five consecutive days. Earlier this year, members of the EIS union voted to lower that threshold to two days.
Mr Flanagan said that although pay and conditions were a factor in some cases, many councils had reported difficulties in sourcing supply cover even when paying the full rate for longer-term vacancies.
"A national staffing standard which factored in additional staff cover would be an approach worth considering," he said.
Mike Corbett, a national executive member of the NASUWT Scotland teaching union, said that supply staff "needed to feel they were not being treated as second-class citizens".
"The most obvious manifestation of this is the continued discrimination against experienced supply teachers in terms of their pay for short-term engagements. However, we are also getting evidence of supply teachers feeling less support in terms of Professional Update compared to other teachers," he said.
Mr Corbett added that the continuing high cost of fuel could also discourage supply teachers in rural areas from taking on short-term engagements.
A Scottish government spokesperson said staffing levels in schools had been broadly safeguarded for the past three years.
"We recognise that schools and local authorities have faced challenges securing supply cover and that's why the most recent Scottish Negotiating Committee for Teachers pay agreement made changes to the pay for supply teachers," they added.