Supply teachers are already vanishing from some local authority lists, forcing primary headteachers back into the classroom and secondaries to continue their subtle manipulation of timetables to plug gaps.
Primary heads in Glasgow say "there are just not the people out there" to provide long-term cover for maternity leave and sickness. One class has already had five teachers since the start of the term because of the vagaries of cover. Supply staff can pick and choose where they go and when, working one or two days here and there.
Heads and local authorities suspect the new probationary system may have affected the lists as teachers who are looking for permanent contracts and prepared to do supply work fear jobs are drying up, and move on to other careers. The picture is not uniform across authorities and some such as Aberdeen and Midlothian report "slightly better" than normal positions. South Lanarkshire, with a large pool of teachers on permanent supply contracts, has no problems.
But in North Ayrshire, Brian Gardner, head of educational resources, said the authority's normal supply list was down by about half. "We are on flashing amber, not quite red alert. If we got a demand this week for six supply teachers in primary, we would be struggling. This is before the winter and the normal bouts of flu," he said.
North Ayrshire anticipated it would have more supply staff available this year because of the probationary system but has discovered the opposite.
"It's not clear why we are tight in primary and secondary," Mr Gardner said. One reason may be that all the additional initiatives in education may have swallowed up available staff. A consequence of the staff shortage is that the nationally agreed 12 full days in-service for the authority's 65 probationers is being reviewed. There would be no one to cover the classes.
Meanwhile, Sandra West, spokeswoman in Glasgow for the Association of Head Teachers in Scotland, said: "There are problems short-term and long-term. All the probationers and people out there are already in classes. Heads are teaching because they cannot get someone to take the classes and this is happening far earlier than normal. It's usually November and December before it affects us."
Elsewhere, Dundee is "already running into trouble" in secondary where mathematics, modern languages, craft design and technology, and computing supply teachers are thin on the ground. "We're going to struggle in January and February," according to Sandy Weston, education resources manager.
In Midlothian, primary "is the best it's been for a number of years," says Donald MacKay, education director. But secondary is "tight" in computing, English, religious and moral education, and home economics.
At least three other authorities are struggling to find home economics teachers. In Falkirk, the council is finding it difficult to get primary teachers and long-term cover as people only want to do odd days rather than whole weeks.
Perth and Kinross has taken on 50 probationers and placed 70 extra staff on permanent contracts and describes the position as "not too bad". Maths and science are problem areas in secondary.
As ever in Highland, "things are no better" in particular secondary subjects and in certain areas such as Caithness, parts of Lochaber and Ross and Cromarty.