Scotland trade union's concern over supply teacher numbers
There are fewer supply teachers across Scotland to fill gaps in the classroom rota caused by sickness, training courses and other absences.
Several councils have told BBC Scotland there has been a drop in the number of supply teachers registered locally.
Scotland's biggest teaching union, the EIS, claimed the situation is at crisis point.
It argued the main reason is a cut to the amount some supply teachers are paid.
Another reason may be that more young teachers are now getting full time jobs so are not available for supply work.
Whatever the precise cause, the practical impact can be a serious challenge. At Marr College, a secondary school in Troon, three of the eight English teachers are currently off.
It has proved impossible for South Ayrshire Council to get adequate supply cover. So first, second and third year students are not getting as many English lessons from an English teacher as they should be.
Instead other teachers - such as modern language teachers - are looking after some English classes as a temporary solution.
The council hopes to recruit three full-time English teachers - who'll initially be used to cover the gaps at Marr College - within the next few weeks.
Most supply teachers are called in to cover for a few days when a regular teacher falls sick or goes on a training course.
Protracted problems quite as severe as the one at Marr College are likely to be relatively uncommon although the EIS said it has "significant anecdotal evidence" from members about secondary schools where children are not being taught by subject specialists.
Nationally the EIS believes more than a third of supply requests and are not being met and that students are losing out.
General secretary Larry Flanagan said: "That means that pupils are not being taught by subject specialists or they're in extended assemblies or sometimes they're sitting in the canteen being supervised because no teacher is available."
Mr Flanagan believes a substantial cut in the rate of pay for supply teachers who are engaged for less than 5 days has had a significant impact. They get around half the daily rate given to teachers called in for longer.
Problems providing cover can be most acute in rural or remote areas or with specialist subjects at secondary schools.
BBC Scotland contacted all 32 Scottish councils and a number said they had noted a drop in the number of supply teachers registered with them.
Edinburgh said there had been a reduction in their ranks from about 950 last August - to 775 this year. But the council says it has been actively trying to find replacements for the registered and doesn't expect problems this year.
Stirling Council said: "We are currently experiencing difficulty in the primary sector and also in with subject specialisms such Physics, Maths and Home Economics in secondary sector."
Perth and Kinross Council said: "The change in terms and conditions for supply staff has reduced the numbers that are available and we are currently trying to recruit supply staff. The availability of supply staff has further been restricted by providing cover for a higher than normal number of maternity leave.
"The main impacts are the amount of time head teachers and deputes are spending covering primary classes, and in secondary schools that subject classes may not always have a subject specialist available."
East Ayrshire said it had experienced some difficulties, particularly in remote rural areas and some specific subjects.
West Dunbartonshire said: "Over the last few years we have noticed that there is less availability on our teacher supply list. As a result of this we advertised last year and also refreshed our list to ensure that it reflected people available for work.
"As with all other authorities we are experiencing difficulties in obtaining supply staff - especially within particular subjects in the secondary sector."
As well as pay, there are several possible reasons for the drop in the number of supply teachers - one of them the unfortunate by-product of what most would see as a positive development.
More newly-qualified teachers are now securing permanent positions so cannot do supply work. In the past, more may have joined the supply register because they could not get a full-time teaching job.
'Impact of pay agreement'
Another reason may be changes to the curriculum. Some supply teachers may have dropped out because of these. And, of course, some supply teachers have simply retired.
But what might help solve the problem?
Many councils are actively trying to recruit more supply teachers while improvements to workforce planning could help sort out gaps caused by planned absences such as maternity leave.
Neighbouring councils might also be able to work more effectively to co-ordinate their banks of supply teachers.
Education Secretary Michael Russell said: "The Scottish Government has tackled teacher unemployment by cutting student teacher numbers, leading to an improving picture across the country.
"However, we recognise that there are challenges in relation to supply teachers, including the impact of the last pay agreement negotiated through the Scottish Negotiating Committee for Teachers (SNCT).
"We continue to involve teaching unions and other stakeholders in workforce planning discussions with a view to ensuring that we have the right number of teachers for our schools the length and breadth of Scotland.
"I am on record as having said that the SNCT needs to look at the supply situation again, and I understand that, while negotiations are on-going, there is a new pay agreement on the table which will address this specific issue."
The current pay offer from Cosla means supply teachers would start to be paid at a higher rate after three days instead of five.
In the meantime practical problems caused by specific shortages - such as those at Marr College - continue.