An open letter to Scotland's education secretary, Shirley-Anne Somerville, has highlighted concerns that teachers are having to take extra jobs to "pay our bills and put food on the table".
It also says that many teachers are essentially on "zero-hour contracts" as they face up to the "casualisation" of the teaching workforce.
The Scottish Temporary Teachers group says it represents over 2,000 fully qualified Scottish teachers who have been "unable to secure permanent employment because of local authority policy and practices".
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The letter refers to teachers from the group having met former education secretary John Swinney last July, but complains that there is still a lack of progress in "the disgraceful way teacher recruitment has been addressed in recent years".
It acknowledges that the Scottish government has put funding in place for extra teachers during the Covid crisis, but adds that such posts "were only so readily filled [as a result of] unacceptably large numbers of qualified teachers unemployed at the time and desperate for work".
Teachers struggling on temporary contracts
The letter adds: "It should also be noted that these posts have been created on a temporary basis. Some are being terminated in June this year, while others will only be extended for one more academic year."
The group also highlights that "many teachers have found themselves working in multiple schools and covering a number of classes (in some cases working in 12 different classes in the space of a week, heightening the risk of [Covid] infection)".
The group says that local authority budget cuts have led to "even fewer posts being advertised, at a time when our pupils need our support most", pointing to one council where only supply work was advertised and hundreds of teachers have been told that their application will simply be kept "on file".
More generally, the group criticises a tendency in Scotland towards "filling classroom numbers to capacity and reducing the number of teachers to a skeleton staff", leading to "classes across Scotland [that] are bursting at the seams".
The letter states that many teachers are being "left to rely on supply work and are essentially employed under zero-hour contracts", adding: "There are thousands of teachers who cannot secure mortgages or car loans, plan maternity leave or make long-term commitments due to the uncertainty of our employment.
"Those of us unlucky enough to be on temporary part-time contracts...have had to seek additional employment elsewhere just to pay our bills and put food on the table.
"Sadly, many of our colleagues have even had to leave the profession due to the instability of employment. Understandably, many of our colleagues have reported a decline in their mental health and increased stress and anxiety levels due to the casualisation of the workforce."
In outlining priorities for the first 100 days of government last month, first minister Nicola Sturgeon said that councils would receive the first phase of funding to begin to recruit 3,500 additional teachers and classroom assistants; she later clarified that this initial funding would pay for 1,000 teachers and 500 classroom assistants.
Today, a Scottish government spokesperson said: "Teachers are working incredibly hard to support pupils through these extraordinary times. We value, and thank, all teachers for their professional contribution.
"Whilst local authorities are responsible for the recruitment and deployment of their staff, the Scottish government believes that we will need all possible teaching resources to compensate for any loss of learning suffered since the start of the pandemic. It is for that reason that we have provided over £200 million to local authorities for the recruitment of additional education staff to support education recovery.
"In the first 100 days of this parliamentary term, as part of our commitment to recruiting 3,500 additional teachers and classroom assistants, funding will be provided to local authorities to increase teacher numbers by 1,000 and classroom assistants by 500."