This suggestion from Ben Lev addresses a problem that I am sure most of us have without even being aware of it:
Yesterday in the middle of a story I was getting great response from the same handful of students and mediocre response from the large middle group. I explained in English to my student Z. that he was doing a great job, that I wanted him to think about the response but not say it, that he had already earned his high marks on the jGR. I showed the class this gesture: 1) I pointed to Z, 2) I gave him a thumbs up, 3) I put my thumb and index finger together and slid them along my closed lips indicating that I wanted him to be silent. I suppose an index finger perpendicular to the lips (shhhh gesture) would work too. Z. smiled and held back. I continued the story and immediately noticed a significant jump in responsiveness. I gave the sign to three more students and continued the story. Response continued to improve, it was amazing. I think it worked bc I was able to “filter out” the stronger students’ voices by silencing them, and making the rest of the class very aware that I am listening carefully and expecting them to step up, no longer giving them a place to hide with their soft voices or non-responses. Just a little trick, but great results.