It's been awhile since I've read this book and I really want to read it again. All I can remember of this book is as follows.
The kid doesn't want to be a mage/wizard.
Kids are tested to see if they have magic by being brought into a room with a bunch of mages/wizards. They turn off the lights and make a bunch of fake magic happen, like flying crystal balls and such, but off to the side, they rip a leaf off of a plant and use magic to heal it and the kid sees it, which was the real test, because only mages/wizards can see magic.
He's apprenticed to and old man who gives him a cocoon to study, to start learning magic as they travel.
He's able to conceal himself from detection, using the magic he learned from study of the cocoon.
And he heals someone important at the end while everyone around him argues. I don't know if the argument is about trusting a mage to heal them or something else, and after he heals them, he walks away.
And that's about all I can remember from it. It's been awhile.