Practical skills. For example: Doing shopping, ordering in a restaurant, using a bus, driving a car, calling a repairman, finding an apartment, buying a computer, paying bills, cleaning a room...

Lots of kids aren't prepared for independence because they don't have all the little miscellaneous skills that the world just expects you'll somehow pick up. And a lot of the time, it's just a matter of somebody showing you how it's done. Whether they will move out or stay with their parents, the more things they can do, the more they'll be able to do for themselves.

As for the classroom environment itself: Keep it quiet, orderly, and make sure they know exactly what the rules are and what to expect if they break one.

Make sure they have time and opportunity to use their strengths and their interests. Some kids, for example, will be great at math and horrible at writing (or vice versa or something altogether different). There's often an impulse to spend all the time working on weaknesses; but don't do that. Let them specialize--work on those strengths, because that's what'll get them a job later.