I am playing the NDS version of Harry Potter Years 5-7 (specifically, Year 5: Chapter 3 - The Weasley Twins Leave Hogwarts) and I am at the point where I have to duel some people (I honestly can't tell precisely who - Sytherins? Possibly Malfoy and his cronies? It's hard for me to tell.).
Problem is, I know -how- to duel (point in either direction and press X to cast a spell, try to hit the other person so they run out of health first) - but I can't actually manage to win the duel - it seems that no matter what I do (cast quickly, or cast slower and build the spell strength) I lose the battle, and have to duel over and over again with no result.
Without winning, I apparently cannot get any farther in the story.
What am I missing here? What sort of strategy is successful?