I saw a really fun tweet from Dave Richeson last week:
I thought that editing this “proof” would be a terrific exercise for my younger son. We started the project by walking through the “proof” to make sure he understood what he was supposed to do. After this short introduction he worked on the editing off camera for about 10 min:
After working through Dave’s document, here are the changes my son suggested:
I think the above video shows why this editing exercise is such a nice idea. There were a couple of points that I wanted to add to my son’s notes, so we talked through two specific ideas to end the project:
This project was really fun and definitely something I wouldn’t have ever though to try. Thanks to Dave for sharing this terrific idea!
Mike's Math Page 
I think this was really useful. I went through it with my 11 and 13 yo in phases:
(1) critique the original mistake filled version.
(2) write their own “perfect” versions.
(3) watch the video with your son’s comments, then discuss and see if we spotted any further problems.
(4) watch your comments and discuss again.
(5) re-write with the intention of incorporating all the notes from 1,3,4. We are using the AoPS TeXeR tool so that they can practice basic LaTeX.
As a final step, I will show them my own version.
I would love to find more examples to repeat this in a couple months.