Harry Potter for Kinect

To unlock this achievement you need to defeat one opponent in each of the four blackboard dueling groups. The blackboard games are unlocked by completing the main storyline. The four blackboard dueling groups are as follows.

Students, Dumbledore's Army, Hogwarts Staff and Order of the Phoenix.

There are multiple opponents for each group but you only need to successfully defeat one for each group for this achievement. I found a very repeatable and effective method for all these duels.

Select Incendio as your spell. Cast at your target, wait about 3 seconds then cast again. The opponent will block the first cast with Protégo. This will break their shield and the second spell will hit and cause damage. The first spell that they blocked will be sent back to you so make sure you sidestep to dodge it. Rinse and repeat for easy wins against every opponent.