Todays Best practice: Dismiss each row one at a time and stand at the end of the row collecting each paper.
You have to make it clear that the HW is due at the end of the period. Today they could work double-time on unfinished HW while watching a Bill Nye video. This kills em, they rather watch the movie.
I dimiss the kids who did the work on-time first. I can tell by the stamp I put on their papers at the beginning of class.
If possible I make them stay a few minutes after the bell... Like a micro detention. They hate this. Hopefully they'll do it on time from now on.
Hope this helps,
Love to Teach and Teach with Passion
Remember...It's not Magic, It's Science