Gary Rubinstein has a good discussion of how to tell if your students are getting in. Don’t just ask if there are any questions.
A lot more effective is to make up a question and ask a random student. If the random student gets it right, there’s a better chance than if you just call on the kid with her hand flailing. (At the bottom of this post I have a cool way to use Excel to generate a random name list)
If you really want to know if everyone gets it, you should ask one of the weaker students a question. If that student knows it, it’s likely most of the class does. I like the random student better since I don’t want the weaker student to think I’m picking on him.
But the best, and most fun for the students, way to instantly assess your entire class is to get a class set of mini-white boards. These are the greatest. You give each kid an 8 by 11 white board with a pen and a little eraser. Then you ask a question and have the class write their answers and hold them up. It’s like a game show.
Of course these questions need to be pretty low level on Bloom’s Taxonomy questions, but that’s OK. It’s still a great tool.
He also has a place to get cheap white boards. Very cool.