And they come up with this. Behold the power of video.
Is there any doubt that this kid understands how to create a sine/cosine function to model a situation? She struggled a bit when this was on the checkpoint in class, but one week later this video shows up. And it has been obvious in the discussions since that she understands this really well now.
So, how is the whole "focus on the content and not on the grades thing" going? Do you even have to ask?
Ask the kids to learn the material and to demonstrate that they have. Then, prepare to be impressed.