Need the title of another book?

So when i was in elementary school I read this book about a kid that had to get injections every week. A lot of the kids at this school had to get these injections. Once day one of the kids at his school disappears and no one knows where he went. He somehow comes into possesion of a metal gauntlet that shoots Bearings out of the fingertips when he extends his fingers. Later on he finds out that he is part of an alien race that has come here to take over the planet. THe injections he was get were to keep him in human form, however these injections dont work when you go through puberty so the kid that went missing actually turned into an alien all at once and almost died. They have to take a test to use the guantlet by shooting cans down, they have to hit 5 cans with one shot (hit one can with each finger tip). They get a new glove that can melt anything (not burn, melt) the glove even metled wood. At the end he rebels against the aliens and claims that he is human at a press conference even though he clearly was an alien.