I agree that comics can be a powerful, positive resource for teaching kids how to read.
In the seventies I was exposed to overwritten comics such as Killraven, Jungle Action and X-Men, or, as I discovered, basically "How to increase your vocabulary by reading the florid prose of Don and Chris". I never read many novels outside of a school course, and yet I could pass my language and literature exams at top grade quite easily.
It's important to read the right material, as, in the nineties, the same exponential increase could not be replicated by reading books from the original incarnation of Image Comics, where words were extraneous.