Classroom clocks tend to encourage non-motivated students to pack up early. So, I covered mine. Next year, I'm thinking of putting a message over the clock. Maybe, "Time to Think." I heard of a teacher who just covered the clock with, "Now." I like that one too. I'm also considering fabricating my own digital clock that messes with my students' heads a bit. The clock will go forward at double speed for the first half of the period and then it will go at half speed for the second half of the period.