I frequently write about and talk about the benefits of using backchannel tools like TodaysMeet in the classroom. Some of my favorite backchannel tools are featured in this guide. Here's a cautionary tale from my early days of using backchannels in my classroom.
Four years ago I had a short (15-20 minutes) video that showed to students in my Civics class. For some reason I got the idea that I would award a bonus point (added to a quiz I recently gave) to the first student to correctly answer the questions I posted in the back-channel. In hindsight making chat a contest was a very bad idea because most of my students either posted guesses as quickly as they could or they tuned-out because they didn't think they could answer quickly enough. In the end, because of my mistake, my students didn't pay attention to the video as well as they would have otherwise. So while a back-channel can definitely improve the educational value of showing a video in class (case in point here), it must be done correctly.