Let’s imagine, for a moment, that the flexibility the OP desires is in place. That means that for every school in the country, there is flexibility for any parent(s) to remove their child(ren) for a specified or unspecified amount of time.
So, on one Monday morning in October, a class of nominally 30 children has 17 in class, because 13 are absent. On Tuesday, 5 return and 3 are absent. On Wednesday, 6 more return. They’ve been off for varying amounts of time.
Leaving aside the variation in the ability and progress of every cohort, how is any school, or any individual teacher, going to plan, monitor and evaluate what those children are learning p, what progress they are making and how to measure all of that in line with government edicts.
Oh, by the way, what is sauce for the goose is sauce for the gander, so 5 out of the 15 teachers are having their holidays this week too.
Everyone knows that the education system is underfunded, under resourced and often under appreciated. Everyone knows that it needs more money, more training, more access for SEND in particular. I hope everyone knows that the majority of schools, colleges and teachers do their best for the young people in their care, under a system that is stretched to the thinness of tissue. Please tell me OP, how your notion is going to make a positive difference to that.