One of the challenges of learning (or teaching) the command line is that different operating systems have default access to a command line terminal, whereas others will not (e.g., Windows versus Mac versus Linux). In a classroom session, this is especially frustrating, because time must be spent bringing all computers to the same starting position. Browser emulator Codecademy offers a fantastic alternative to this challenge because it has a terminal emulator directly in the browser, so you can practice and execute all the commands in the emulator, regardless of what operating system you have.
https://www.codecademy.com/learn/learn-the-command-line
In practice Another feature of codecademy command line interface that I like is that tutorials have students first implement a command, then afterwards there is an explanation of what the command does. This allows students to practice first, observe what happens, and then read through a detailed explanation.
So far, students in the lab have liked this tutorial. We start with Codecademy, then work on installing local terminal/Linux-like environments (e.g., cygwin for people with Windows machines).