I've been waiting for people to figure this out. It's not just kids who have shorter attention spans. Though I am blessed with friends who still call me "young

I've been waiting for people to figure this out. It's not just kids who have shorter attention spans. Though I am blessed with friends who still call me "young man", I'm no longer a kid, and I'm a veteran of many years of lecture-based courses. But that era is over. There's no longer any technical reason to deliver lectures in uninterrupted fifty-minute blocks. And it turns out that they only reason I ever liked that format is that I didn't have alternatives. I've attended so, so many physics lectures. They break naturally into chunks: Some scene-setting ("let's talk about conservation of momentum in two dimensions"), proposing a problem ("here's an ice rink with two hockey pucks that collide"), a derivation (equation, equation, chalk dust, erasure, equation, more chalk dust, fix the sign error), a summary ("look, momentum is conserved! And we can draw the following general lesson..."), questions from the audience, and finally a bunch of homework problems. How great it would be to have each of these chunks be recorded as separate bits of video. You could play through the scene-setting and the summary multiple times. You could play through the derivation at higher speed, slowing down or repeating the bits where the prof makes a subtle point but speeding through the parts which are obvious to you. You can skip the student questions that you already understand but play through the subtle ones more than once. About the only disadvantage of this way of learning is that it's kind of isolating. It would be nice to combine it with lots of lab-type gatherings where all the students can join together and feel like a team. --- [1] I had a few professors who avoided using chalkboards. They would provide handouts with the day's derivations and equations on them, then use an overhead projector with slides. (This was all before Powerpoint was widely available in academia.) This was a mixed bag. It worked okay, but it wasn't an obvious big win over chalkboards. One advantage of the chalkboard is that it is very flexible: you can gesture at it, redo it on demand, or scrawl circles and arrows all over it. Another advantage is that it is typically huge, offering you lots of opportunity to, say, write Maxwell's equations in a box to the left and leave them up through the whole lecture for reference. Finally, chalkboard derivations go up slowly (sometimes really slowly, if the writer is not well practiced), which can be bad, but which also makes it easy for the professor to interject meaningful comments. But I think the availability of digital video playback, cheap cameras, and nonlinear editing changes this problem a lot.