I'm diagnosed with ADHD (ADD). The live person speaking and often gesturing while talking is much easier to focus on and fill in the frequent gaps where focus drifts. Something about the talking with minor stops and pauses gives more frequent opportunity to regain focus control and begin contiguous focus briefly before repeating. I was able to successfully get through schooling and college isolating classes with teachers that talked through concepts but failed frequently at classes focused on books and static mediums.

With online, it's brutal trying to retain focus at a monitor and reading while retaining. The focus drifts in and out unconsciously so you can read an entire page of text before realizing you retained literally none.

For text based learning I often need to dedicate a large amount of time "re-reading" material in advance to improve retention during the live discussion part if it lacks enough depth. Calculus was the critical crux of my educational path.