If you'd like to reduce the frequency of this question being asked of you by your students, you might want to try out the magnetic tile strategy a friend of mine uses with her fourth grade class.
The big benefit here is that students are given the opportunity to develop a bit of self-direction. As opposed to asking the teacher what to do, the student makes the choice himself. Adding to the effectiveness of the strategy is that there weren't any "goof-off" choices. The three options available in the grid were all academically meaningful.
It's this kind of "freedom within framework" that really helps students become independent. And as the number of students in a classroom continues to grow, the need for students to exhibit independence and self-control becomes even more critical to the overall success of the class.