Codecademy
Pros:
Courses tend to be very accessible (easy to get started and provide a quick remedy to apprehension a mentee might have about something being “too hard”). You can work through the material in-browser without any local setup.
Cons:
Quizzes and projects are “Pro” features and are not free.
Many of the “cons” for Free Code Camp apply here as well, as both take a pretty similar approach.