Any ideas for motivating high school classes to turn in all their work?

I get high turn-in rates for major assignments, but when it comes to smaller ones (I'm not talking about busy work, mind you) I find that it's harder to encourage students to turn them all in, and on time, for that matter.

I already allow late work for 75% credit up until the end of the quarter, which I think is more than fair. I rarely give "homework"; my classes generally just have to complete any work at home that wasn't finished in class.

Does anyone have anything fun/positive that they do to encourage high turn-in rates?