Nah, they're pretty different. The entire structure of the stories is vastly different; the only similarities are (a) it's set in a school, and (B) there's a hidden magical world with mages/wizards. Oh, and both the characters are orphans.
EDIT: Okay, the old-mage-headmaster is a fourth similarity.
Now, Emily Drake's series - THAT is Harry Potter set in America. And if she could do it without getting flak from lawyer-types, Akamatsu has nothing to worry about.