When teachers put students in groups and ask them to complete a task – designing a poster, discussing a reading text etc. – they can be sure that some group will finish before others. If the activity has a competitive element (for example, who can solve a problem first), this is not a worry. But where not such element is present, the teacher is put in a quandary: should he stop the activity (which means not letting some finish) or let the others finish (which means boring the people who finished first)?