I've been thinking about that on and off for years, and I think the most important factor is the teacher's apparent level of respect for the students. In the classes where the students actually worked, the common thread I noticed was that the teachers of those classes visibly expected the students to work hard and do their best. And vice versa: the teachers who were the most obsessive about controlling their classes were also the ones who got the least cooperation in this from the students. (I think the causation goes both ways here.)

So if I were teaching, say, a math class, and I wanted to use Sal Khan's videos for the lecture content, here's what I would want to do:

1. Have less class time. They're watching videos outside of class, so it all balances out, and makes the videos seem like a more legitimate part of the class.

2. Let the students know that, if they just cram before tests and don't watch the videos, they'll probably flunk. Contrariwise, if they keep up with the work, they should do just fine, and if they're having trouble, I'm happy to help.

3. Keep grading standards high enough that the preceding statement is true.

4. Have the first test be difficult but not weighted heavily, as an official kick in the pants to stir laggards from their lethargy.

I think this would go a long way toward creating the right mind-set in students, if it's matched with the corresponding respect from the teacher.

Is it as simple as the student liking or being interested in the subject?

I like math, I worked hard, paid attention and learned as much as I could.

I wasn't nearly as interested in what was taught in my English classes, so I did everything at the last minute, and did just enough to get the grade I wanted.

I think past 10th grade or so, the value of forcing a wide liberal arts education on people declines significantly.

Different people are interested in different things. If a student just does not care about math, they're going to devote a lot more of their effort to their science classes and do the bare minimum to pass in Algebra.

They don't see the relevance of that class, the class isn't as important to them as another class, etc. Tons of reasons they might deprioritize on class over another.

Ive dealt with classes and have seen both types as well.

One hypothesis is it's the energy between students and professor: Ones with higher energy in the class make change faster. In order to keep up, you have to think and do faster.

Then I've been in classrooms where the professor did not want to be there. He knew it, the students knew it, and the interactions cemented it. The 'energy' was completely in the shitter. At best, it was rote memorisation and drudge work. Big surprise: most of the class slacked off and cheated, and did the 12 hour cram before tests.

There is the 3rd category: in which the professor cares, but the student had to take this class for one reason or another. The general idea here is the student only minimally cares. I've seen this, where the student says to others "I dont care as long as I get a C." I'm guessing these are the most infuriating to professors.