What predicts success in class

A couple years ago I listened to a keynote speech at a NC community college system conference (statewide teachers conference) by a gent who had visited 1,600+ colleges to learn how things were done.

One of the things he talked about was the best predictor of success in college classes.
It is not SAT scores or "IQ".
It is not high school grades.
It is not family history.
It is not family income.

It is how well the student attends classes.

This matches my experience. It is worth telling students, who often have the notion that they can miss class and not really miss anything. (Students will thoughtlessly insult the instructor by coming up and saying "am I going to miss anything by leaving an hour early"? Or, "did I miss anything when I wasn't here Tuesday?" What, we often don't do anything important in class?) I tell students at the beginning of a course that I talk about a lot of things that aren't in any textbook, and that we do a lot of hands-on or group activities. These are things that cannot be "made up", especially in our age when students are inattentive and frequently don't write down any notes. In the past I usually included in the tests questions that were easy to answer if you were in class, but not easy if you weren't (and so hadn't participated in the problem-solving sessions). This semester I have "canned" tests (which I strongly dislike, as they tend to be tests about the textbook rather than about the subject), but I intend to work questions about problems we encountered in class, and discussions we had in class, in there some way.

Obviously, I don't teach the way some classes are taught in universities, where the professor walks in, lectures (all one-way) to a few hundred students, and never even learns their names. There the students can get recordings of the lectures and know almost as much as if they had been there, and some schools produce podcasts of lectures for that purpose. I try to discuss things with students, which doesn't translate well to podcasts, though I sometimes record myself using my Sansa MP3 player. Younger students, in particular, strongly prefer interaction during class, rather than "lectures".