Yeah, the deal with classroom management is besides taking practice, it seems difficult to tell who has classroom "presence" and with what age groups short of putting them in the classroom and watching what happens. Granted, substitute teaching (as opposed to full-time) lets you back out fast if it doesn't work out, so there's that. I'm good with high schoolers, middle schoolers drive me nuts, and I would flat-out refuse to teach elementary school unless there was an emergency.

Anyway, good luck!