HP: I figure that Muggle schooling would only be for Muggle-borns (duh) or halfbloods, who have one foot in both worlds to begin with. For one thing, given how hopeless the Weasleys are with the most basic details of Muggle life, I can't imagine a wizard or witch being able to successfully register their son or daughter for Muggle school without a Muggle's assistance. ("Psst! What's a te-le-phon-e? And why've they got numbers?") So a Muggle or Muggle-born parent is required, meaning that the kids in the household are probably aware early on of the difference between Muggles and wizards, and may have learned very quickly that there's certain things you Just Don't Say to Grandma. For another thing, there are probably some magical families who live smack dab among Muggles, not out away from them like the Weasleys--probably the same ones with Muggle or Muggle-born parents. They wouldn't be able to get away with too much magic in plain view of everyone, meaning that there would be less for the kids to potentially reveal. In fact, I can see a witch or wizard with a Muggle spouse and living among Muggle neighbors concealing most magic from his or her kids until they're old enough not to blurt out every damn thing they hear or see.

Dice: There's a reason that dice are made from the regular polyhedrons (aka Platonic solids): the overall symmetry helps guarentee that no one face is more likely to come up than any other. Therefore, ensuring that each roll is as truely random as possible is just a matter of cunningly arranging the numbers on each face. d10 are a bit more complicated than that.