I use homework as motivator for students to study by allowing them multiple chances to improve their homework score with repeated attempts. To get the maximum score, the first attempt must be turned in by the due date; points are lost from the maximum for each day that first submission is late. Using on-line tools gives the assignment an "entertainment" aspect, like a trivia game, as they try to beat their best score. The repetiton enhances their familiarity with the material. Because of this, I find it counterproductive to let lateness drive a possible score down to zero - they lose that motivation to study.