My son is just entering K this upcoming week, so we've not yet moved. But we didn't get into the public elementary that we wanted, so he's on the waiting list. He knows that if his name comes up, he'll be moving. He's prepared for it, and will probably be ok with it. I woudn't switch after mid-year for an older student, IMO that would be hard for the student unless things were really unmanageable at the school. And of course the older they get, the harder the change might be during the school year. But overall, finding the best school for the child is paramount, even if that means changing mid-year.