Sometimes it's ridiculous-- my then-4th grader was taking Algebra I on the side, and had shown mastery on the 4th grade fraction curriculum on a test, but getting the large packet of fraction work that he missed during an absence was considered critically important. :P

> reveals that schools are talking bollocks when they suggest that taking a few days off to go on holiday during termtime

I do think that the kind of attitude that lets you ignore a bit of schooling here and there for a convenient vacation schedule does affect outcomes, though. I teach at a private school, but I think we're both aware of incentives for attendance, the reasons for them, and the areas in which they cause perverse outcomes.

But it does seem true, from the point of view of parents and children. It doesn't matter that the curriculum is helical and revisits the same topics multiple times. It doesn't revisit the same topics multiple time in a single semester, which means the kid doesn't get a second chance to learn a topic within the grading scope, which means they have to catch up or risk a lower grade. As much as we say that it's the education that matters, as much as it should matter - it doesn't. What matters are the grades. At the very least, in my experience, most parents have grade expectations, and the kid will suffer negative consequences this semester if they fall back, even though they may recover by the end of the education level (where again, the final grades are all that matters).

(Even though the immediate pressure may come from the parents, it's in a control loop with the grades, so the school can't pretend this is not happening.)