Every Friday, I set aside a period of time (about 1/2 an hour) for "Fun Friday", during which time the children can have free time for an activity of their choice (board games, and creative materials are available, as well as the classroom library and exploration centers). This time is automatically theirs, unless their behavior during the week interferes with the completion of a lesson or an independent task. If a student fails to finish an assigned task to the best of their ability in a reasonable amount of time because of behavior issues (NOT ACADEMIC DIFFICULTY, OF COURSE!), the assignment goes into the "Fun Friday tray". At the beginning of Fun Friday each week, I distribute unfinished work, and those children have to complete the work before they can play. It's a real consequence, rather than an arbitrary punishment, and it really works!