Why don't school have more double periods?

[Coolingfan]

I'm in Scotland - kids back at school.
DS has swimming for the first block of PE. Said they didn't get very long in the water due to having to get changed into/out of costumes and rush to next class.
Got me thinking - why don't schools make more use of double periods for practical classes- PE, science, home ec, technology etc. Instead of two 50 min lessons make it one 100 min lesson a week.
Seems logical to me - do your kids' schools use them, or is it a logistical hassle for them? Maybe it'll happen in the later years.

@BernadetteRostankowskiWolowitz have you ever tried to work out a school timetable? Seriously, that's never going to work!

Split classes are tricky but absolutely the two teachers should communicate properly. We tend to sort it out between ourselves either one lead teacher tells the other what they want covered in a particular week or topics are split and we work independently. Which option is best tends to come down to teacher preference / the topics / the lesson split / time I’d say if lessons / type of class. What really shouldn’t be happening is a lack of communication that means students are effectively missing a third of their teaching time.

They probably want the whole year group do to the "end of block test" at the same time.
Yes, maybe. Though the ones who have been watching science videos may be at a disadvantage.
Which reminds me - in English the whole year group were reading a novel but DS class got behind somehow - so, if they could, they had to try to watch the film version at home to catch up.
Sanity - in S2 (year 8 for the English amongst us)

@Coolingfan most sciences classes are on some sort of rota for lower school science. The test reply (all the students having covered common topics) is also a valid one.

*time of day of lessons

The end of block test being fixed can be a constraint but even within the same topic there are usually streams that can be selected out for one teacher- or key skills such as graph work etc . It doesn’t sound like their system is working

I realise it's easy to say "why don't they just do xyz" and not understand the constraints the school has. So these replies are useful - end of block test I hadn't thought of. The school had staffing issues last year which I am sympathetic to.

When I was at school one period was 40 mins I think. So we had many doubles.