Jasper, I have't taught in the UK for a few years, but I am a primary teacher. To answer your question, yes, they do learn something everyday, provided they are motivated (which is also in to a large extent down to the teacher) As others have said, often work builds on previous work, and includes lots of repetion and review, but the repitition and review are essential. To take a simple example, once a child can write their letters accurately, you don't then say "great they know that" They repeat it in everything they do every day, so that they learn to write fluently, confidently and accurately. The daily repetion is such an inportant part of school life, that kids who miss a significant part of it actually don't do as well as those who are there all year.
As well as skills like writing, we teach things like history, science, maths in subject units, and you can miss a whole unit by being away for 2 weeks. There is some repetition of units from term to term and year to year, reviewing the work done before, and building on it. As a teacher, I hated it when someone had been away for 2 weeks, if it was due to illness, I did everything I could to help the child catch up, but I must confess I really resented it when it was due to holidays. The teachers time in the class is so precious, you are always juggling different groups and different children's needs. For each curriculum area missed, that is 10-15 minutes of catch-up I have to do for that child. That 10-15 might have been the time I had planned to sit down with this group and give them a little extra imput, but now I can't, or it might have been the time I would hear a couple of children read. It would mean that I now have to do something in break time to catch up (eg ask kids who don't mind if they would like to stay in and read to me) Now I don't mind putting myself out when necessary, but I do need to go to the loo, and grab a quick cuppa (to lubricate that throat that has been talking all morning) so it is frustrating to have to try and catch up kids who've been away.
I sometimes think, that if you have chosen to take your child out during term time, then you should be prepared to come in to the classroom and help out in the following week to compensate the teacher for their time.
I do understand the problem of holiday costs, but to be honest, most of the kids in my class had a fornights holiday in a caravan in Clapton. (during the school holidays) The ones who missed school were usually off to disney land or somewhere exotic. Nice if you can afford it.