I have to concur. I'm a teacher ed student right now, and I have no idea how you could ever possibly pull that off. If you did, you'd be a bloody superhero. If you really need to work in that regard, just find a govt job or something with the bennies, considering they'd do tuition assistance, possibly.
It's not even that it's the hours of teaching, but seriously, if you're freaking about contracts, or torts, or something, how do you think you'll be able to devote 110% to the children. You're there as a teacher for them, not just to collect a pay check whilst you get your JD. I don't mean to be harsh, but law school and teaching full-time, not necessarily doing sub work, are mutually exclusive, in my mind.