In the UK teachers at state schools have a series of resignation dates: currently (as defined in a document referred to as the Burgundy Book)
|To leave at..||Resignation date|
|31st December (Autumn term)||31st October|
|30th April (Spring Term)||28th February (or 29th)|
|31st August (Summer Term)||31st May|
The time just before Easter and the summer are reminiscent of the football transfer window; teachers can only move at a certain time of the year and they are stuck unless they can find a new suitable position.
In other parts of the world the rules can be more stringent, in parts of Asia teachers can only move during after the summer (and must present their notice the previous December).
The reason football teams have a transfer window is to keep the sport exciting, and to have a settled team for most of the year. This prevents a wealthy team seeing they have a chance of the championship buying players at the last minute to boost their chances.
Schools put somebody into place to be able to deliver classes and lessons to classes. This is important because schools are there for the education of students, if nothing else you need a body in front of a class day in day out. Teachers not currently in a position can be employed outside the resignation dates as by definition these teachers do not have to resign from a previous post; however, there is a fear that these are the dregs of the available talent pool and may head teachers opt for temporary staff when in this position.
It is possible for teachers to have three or more interviews crammed into the last few days before the resignation date as a rushed form of musical chairs takes place. This takes teachers out of the classroom during important revision sessions. Teachers who want to move have a limited time to make their wishes come true, while schools become desperate to fill available vacancies perhaps being satisfied with any candidate on offer.
This March the clamour for the best staff seems more fraught than ever, as teachers who leave the profession are not being replenished by new staff. The Guardian reported in 2014 that 20% of secondary teachers are under 30. Teaching in the UK is becoming a young profession where people stay working for a few years before they can find a career that does not demand a 60 hour working week.