on-What are pre-requisites for teaching version control to a high school CS class? I'm interested in introducing version control to a HS CS class, and was considering starting with Github since it's a fairly standard tool used by developers.

What are pre-requisites for understanding version control that I should make sure students master first?

Any suggestions on other ways to introduce this topic to students are definitely welcome!
The biggest one for me would be a reason to use version control. When you're writing small lab assignments, version control probably isn't worth all that much. It's when they get to a point where projects become larger than a handful of methods, or when you're working on separate pieces of a larger project with partners that it becomes useful. 

Version control, specifically Git and GitHub, is definitely on my list of new topics to add to my 2nd year course next year. My students are doing collaborative projects right now and it's painful to watch them email code back and forth.