Among the Hidden
Among the Hidden Narrator:
Third Person (Limited Omniscient)
Luke Garner has nothing to hide from us—or at least nothing to hide from the narrator, who hides nothing from us. The key ingredient in this narration is that it focuses on Luke's innermost thoughts and feelings. We know when "his brain seemed to be slowing down" (15.8), when "panic [is] welling inside him" (22.23) and we are inside his head when he makes the ginormous decision to get a fake I.D. (29.67-69). We don't get this special insight with any of the other characters.
By getting the inside scoop on Luke's emotions, we can easily identify him as the main protagonist. We're on Luke's side before the action even starts. But at the same time, we experience the other characters through Luke's perspective as well. We know the strict Mr. Garner and the precocious Jen Talbot because that's how Luke interacts with them.