Using these two hand gestures, I am able to see how many students grasp a concept and who may still be struggling. I recently found this great printable on Pinterest that I have since hung in my classroom on our front white board to help remind kids what each sign means.
Find this wonderful printable here: http://mrsgilchristsclass.blogspot.com/2011/10/checking-for-understanding.html
Throughout a lesson, I will ask student to "Give Me Thumbs" to see where they are with their learning. There isn't any movement or sounds required except for the thumbs-up, meaning "I can explain/teach it to someone" of the thumbs-sideways, meaning "I need a little more practice." Oftentimes, kids will move their thumb in between or move it back-and-forth, which is completely okay.
If I notice it may be time for a break, I will have kids pair up and practice teaching it to each other, sometimes using the "Teach-Okay" method from Whole Brain Teaching. Other times, I will have a thumbs-up find a thumbs-sideways and practice explaining it. I also will have all thumbs-sideways and those who are in between join me on the carpet to review together in a smaller group. Lastly, I will just "take the temperature" of the room and make teaching decisions based on the feedback.
One thing I want to point out is that I never use the thumbs-down when it comes to checking for understanding. I want students to feel like they are either getting it or are on their way, not completely lost without hope :)