I have recently been browsing user questions to Khan Academy Videos, because they are pretty interesting. For example, here are some student questions from his video on acceleration.
With these questions, users can vote the question up and down, such that the question “importance” is crowd-sourced.
So where does this fall short?
One reason this falls short is because the bottom question would be (to me) the most generative, interesting, and significant question for my students to pursue. That’s not to say that the other questions aren’t important. Understanding vectors vs. scalars and understanding why division can be thought of as multiplying by inverse are both relevant questions, but those questions are probably not going to lead to interesting pursuits. In contrast, the question of how to find acceleration with distance information is a real puzzle–one that requires some real digging into. The question about velocity and speed are likely the result of that vocabulary being introduced, with “pat” answers that aren’t very meaningful.
Part of the job of me as teacher is see the significance and generativity of my student questions: Does this question concern significant disciplinary ideas? Does it represent a significant difficulty or misunderstanding from which we can learn? Will this question lead to meaningful inquiries? For those purposes, not all questions are equally good and students don’t necessarily have the perspective and expertise to discern the difference.
Not only question, but Answers to Questions
Users can also post answers to questions. Like questions, those answers can moved up or down in importance as users vote on best answers. To follow up on our question, here are three answers to the question about how to find acceleration given distance information.
Why does this fall short?
Of these three responses, the one voted to the bottom is probably the best one–even if you don’t think it’s great, it’s still much better than the first two. The first two simply refer to using an equation and plugging away. The last one, although cursory in exposition, at least leverages the use of an important idea: average velocity.
Additionally, students in physics are prone to “look for the equation” to use. Here we see that the users have simply vote up answers that fits their expectations about what a good answer should look like: It should provide you with the equation to use. Crowd-sourcing might then just be a way to reinforce such views.
Anyway, I suppose I should just add that this isn’t an “attack” on KA. It’s just some thoughts about how teachers vs crowds prioritize questions and explanations for learners.
Teach. Brian. Teach. 
Brian, I really like this activity as one to do with future physics teachers.
You mean, get my future teachers to look at Khan questions and explanations, and discuss the usefulness of those questions and explanations for learners? … That’s interesting… I wonder what prompts, scaffoldings they would need.
I was picturing as using it as a classroom discussion so wasn’t too worried about the scaffolding since you/the instructor would be there to help them get to where you want them to get to.
Learners really like clear explanations, and I’m sure the first two explanations feel both closer to the experience students have when learning physics (in particular students who are struggling and come to the Khan Academy for help) and it feels clearer. Of course, this doesn’t mean that they learn more from “clearer” explanations, they’d probably learn more if they took the time to understand why the answer you highlighted is the best.
The bottom answer may not have gotten the votes you think it should because of the sign error in computing average velocity. Computing average velocity is a good idea, but doing it wrong is not.