re: What is the biggest movie plot hole you have ever seen?

Not a plot whole really but I always wondered why parents kept sending their kids back to hawgwartz. Seems after the first few years with harry there they´d get the point. Also in year like 6 and 7 why does everyone start calling harry a liar. It had been pretty well documented by that point in time that he had saved the school and possibly the human race time and time again.