Off. Eye contact and body language over video are a false proxy; you can't actually read expressions as well, and I find it better not to have the signal than

Off. Eye contact and body language over video are a false proxy; you can't actually read expressions as well, and I find it better not to have the signal than to be misled/mislead by it. Additionally, when teaching online, it's useful to have a way to change the tone; going on camera is really useful for that, and you lose the ability if you start with your camera on. Most importantly though, being on camera and constantly having to model attention is exhausting; we don't require that people seem so ostentatiously alert in real life, and I think that everyone who ever complains of "Zoom fatigue" is actually suffering from "constantly bright-eyed and enthusiastic on camera fatigure". Off-camera, you can pay the exact same amount of attention, but also keep moving, engage in other relevant tasks, read something carefully without appearing rude and so on. Off-camera by default is easier, more pleasant, and more efficient.