Every week, you can be evaluated by Principal Sol, who can change your star rank, title, hat or wand under certain conditions. See Wizard Titles, Hats, and Staves for the conditions and rewards you can get when you are evaluated.
Things you do around the town affect how you're evaluated. If you do nothing but cause mischief (prank magic, you know what I mean), then your evaluation will be bad.
Stuff you can do to improve your evaluation includes;
-Going to class
-Talking to your classmates
-Watering plants/planting things