Re: Actually back in the 1990s I was at a company...
he doesn't go on the "first" day back, as it's an inset day...what the actual...? You've just had x weeks off
(in the UK...)
Blame Kenneth Baker. Yes, it was that far back. He wanted to "professionalise" the teaching profession and among other innovations he decided that teachers should work a fixed number of hours. Up until then teachers had been (to a greater or lesser extent) willing to work enough hours to get the job done. This often involved going into school during "holiday" time, or after hours in order to prepare the classroom or attend a training course. It nearly always involved taking children's work home to mark. Believe it or not teachers are not actually paid during holidays(*) and are not eligible for overtime.
So Kenneth Baker set a fixed number of hours for a full-time teacher. A lot of things changed as a result, not least of which was the introduction of "Baker Days", officially known as IN SErvice Training, or INSET. During a Baker Day, teachers are given time to attend training sessions, CPD, that sort of thing. You know, the sort of thing that you or I would be given time to attend during a normal working day. Most teachers can't do that because they have to - you know - look after a classroom full of rowdy kids. Very occasionally an individual teacher might be given time to go on a course and the class covered either internally or by a supply teacher, but this is expensive so most schools prefer to undertake training either on INSET days, when they can train large groups of teachers together, or in "twilight" sessions, squeezed into the time between sending the children home and the official end of a teacher's day, when they are normally tidying up, marking and preparing for the next day. Of course, many teachers (particularly at primary) also end up taking work home, so the whole idea of fixed hours is a bit moot.
Most teachers are now also eligible for PPA time (this was a Blair government innovation I believe). This is generally 10% of the working week (i.e. one morning or afternoon session) of "non contact" time which is intended to allow an individual teacher to undertake paperwork and other administrative tasks. Good schools employ an additional teacher who covers such time, maybe (particularly in primary schools) by teaching a non-core subject such as music at which the class teacher may not be confident. Not-so-good schools (my opinion) use a "teaching assistant". In theory this time is not the responsibility of the class teacher, but particularly where TAs are used (perhaps less so for Higher Level TAs), the class teacher still ends up planning and reviewing the session.
Teachers do get bad press sometimes, but a lot of it has to do with misconceptions such as that surrounding INSET days. Many seem not to realise - for example - that teachers are not allowed to take their massive allocation of holiday whenever they please, not even a single day. Got a child of your own who is off school sick? Best of luck with that. Even taking an afternoon off to attend a funeral can sometimes be problematic.
Disclaimer (as if you couldn't guess) - I come from a family of teachers and my teacher wife also comes from a family of teachers. I did try it myself for a short time, until I realised I was hopeless at it and couldn't cope with spending four hours a night (requirements for newly-qualified teachers were quite onerous) on marking and preparation.
(*)Well, those in permanent positions do get a monthly salary which doesn't change during the holidays, but it's actually based on the number of hours worked. Teachers who are not on permanent contracts appear to receive a higher salary. In fact they are paid the same as permanent teachers, but the pay is concentrated into the actual working time and isn't spread out equally across the year.