Science is all about asking questions. I try to instill this in my students every day. But sometimes in our class discussions the girls get SO interested and SO curious that we follow a rabbit trail of fascinating questions instead of the well-worn path. For example, without even realizing it we have departed our main topic of the moon's rotation around the earth and are suddenly discussing black holes and what happens to an astronaut if he left a spacecraft without a protective suit.
The parking lot is the perfect way to keep the students on track. Whenever someone asks a thoughtful, content-related question that we just don't have time to expand upon at the moment, I tell her to "park it." (Translation: Write it on a sticky note and put it on our Parking Lot poster.) I keep sticky note pads in little supply boxes on each table, so they are within easy reach. My girls are so used to this process now that many times they won't even raise their hands to ask. Instead of interrupting the discussion they simply get up quietly and park their question on the Parking Lot!
At the end of the week, I choose the best/most interesting questions and answer them on our class Blackboard page, complete with the girl's name who asked, and my answer.