Talk on YouTube from RailsConf KC 2016: https://www.youtube.com/watch?v=59YClXmkCVM
This uses the idea of a nursery rhyme to teach refactorization of code. This is actually language-specific: https://www.youtube.com/watch?v=59YClXmkCVM&t=7m41s
Equivalent to how going through CSE 142 and CSE 143 material and exercises for a language is great practice.
Well, yes, but it's not a matter of whether it's useful - it's a matter of time and progress.