Most schools claim they only consider the highest score, and disregard anything else. Some take an average but from what I've heard, that's rare.
I think having a previous low score can cut both ways... on the one hand, you had a low score which may raise questions about your ability to handle the coursework - on the other hand you raised your score by a lot, which shows you're tenacious and face challenges head-on, blah blah.
I don't know how schools view it. Logic would dictate that it shouldn't matter.