There are lots of philosophies on how to manage student behavior while a substitute is teaching. This is one of the best tricks I've come up with.
There are lots of ways to use them--in a nutshell, have students fill them out w/name (in two places) at start of class, leave on desk during class, and have them complete the questions at the end of class--dropping them off at the doorway when class ends. If a substitute is having trouble with a student, the sub tears off the end of the student and writes their concern on the torn off portion, leaving it with the sub note (helps the sub confusion of which kid is which, who caused the problem, etc after class has ended and they're trying to leave a decent note).
Best way to use them...the long explanation:
I have each student fill one out ahead of time with their name in both places. I check the names when I collect them for two reasons: I want to know that I have one for each kid, and I want to know the real name is written in both places.
Then I make a stack for each hour I teach and when I'm gone I have a reliable student pass them out. If there's no student for a slip, the sub can mark 'absent' on it (saves the sub a lot of headache and time).
I have kids write the date on the back of the behavior slip (only if my absence is for multiple days and they'll have multiple slips to fill out).
I have a bucket by the door for collection and the bucket then becomes a reward raffle when I return. Sometimes the prizes include swag from whatever conference I was at, candy, or a coupon for borrowing my awesome teacher chair for an hour. I always do the raffle but if a student has their behavior note torn off by the sub, their ticket cannot win.
I've found this works well for everyone! My subs have loved it (very little work for them to use it, and if the kids are used to it even better!). I've found it holds my students accountable. It reminds kids that I am "watching" them and so far it has been foolproof!