DD's school have said this, and yes I have checked with the school.
Dont get me wrong, no issue personally with poppies. However I dont think that the school can insist on pupils wearing a poppy to the point that they can be put into isolation for not wearing one, can they?
A poppy is an act of remembrance and if a person has no reason to wear one, or prefers not to, then how is that any of the schools business? I dont wear one, but I buy 2 crosses every year for my grandfathers graves who both fought and suffered horribly during WWII. I remember, I just dont wear a poppy.
DD has chosen to wear one, but says that most of her peers wear them because they have to, not because they care. There have been no assemblies or lessons about why poppies are worn and what the represent so she thinks that in the main this rule is pointless.