Yeah, for me it was the reading, too. In fact, I can't think how it could be any different. I think the constant exposure to written words is crucial. The kids who didn't "get" spelling probably didn't read much, either (or, at least, not as much as we did.)
I wonder now about kids who are exposed to so much internet lingo. And I’m certainly guilty of using the abbreviated forms myself. But if you learn to spell from internet forums and chat and such, you are doomed, I think. Plus the English language has taken a nosedive in general.