I say "and" but really for most undergrad students it's an either/or proposition. Lecture and readings are usually redundant, so the students who attend lecture tend to blow off the reading and those who diligently do the reading don't feel too bad about skipping class. This is a generalization; there are plenty of exceptions, students who attend class and study heavily, or classes where the reading and lecture have no common ground. But in a lot of cases, students are conditioned to study as little as possible, and this is an obvious shortcut that can free up some extra time for, say, playing games.
Without going into a discussion of how to change the culture of an entire generation, let's assume that this carries over into online classes and see what happens.
In the online classes I've taught before, there is no "lecture" per se; the lecture has been replaced by... more reading, which was written by whomever developed the online course. So students have reading from the course website, and assigned reading from a textbook. (Visual learners are probably quite happy about this, while auditory learners get screwed, but I digress.)
To a student who sees this parallel of "lecture == course website" the reading again becomes either/or: read the course website, or read the textbook. Naturally, the website wins, so any assigned reading from a textbook in an online class is likely to get ignored by a lot of people.
I never noticed this until recently, when I was grading an assignment for one of the online classes that I was teaching. Most of the students seemed to not understand a particular concept, the difference between constituative and operational rules from the Rules of Play text. It's a difficult concept, granted, but everyone seemed to be misunderstanding it in the same way. What's going on here? Well, I checked the course website to see what it had to say about this concept... and it just mentioned it in passing, giving a couple of examples to supplement the textbook but not really explaining it properly (probably because the course developer expected that students would do the reading). But here's the thing -- you wouldn't notice that the course website's material was supplemental unless you did the reading in the textbook! So all of these students thought they knew what was going on, even though they didn't.
This is, I think, a major hazard for online course development. Here are a few ways around it:
- Warn students early and often that none of the work in the class is optional. (This probably won't work, but at least it makes it harder for students to complain when you catch them slacking.)
- Force the issue. If the graded assignments directly reference parts of the reading that aren't on the course website, students will have to read at least those parts in order to complete the assignments.
- Tape your lectures and put them online, instead of writing text. This requires some extra equipment and technical know-how (and not all course website packages support all kinds of video), but it does at least make it so that the students aren't just doing reading and reading and more reading. If they don't burn through their will to read on the course website, maybe they'll have a few brain cells left over that are willing to take a peek at the textbook. (Bonus: if you already teach a face-to-face class and tape it, your content is easy to develop.)