Firstly, love the site, I assign many of the sections as homework for my students.
Unfortunately, I ran into a snag this past assignment when I gave the "Make a Website" section as an assignment. I didn't use the Teacher Create a Class feature due to this being a one off assignment. Many of my students ended with zeros or low grades due to not completing the entire skill. Reading through their emails, I found a recurring theme: they stopped because it said "Congratulations".
While it is their fault for not reading the whole thing, many stopped due to the phrase "Congratulations, you completed the HTML section". My suggestion would be to add a minor feedback system that indicates how many steps have been completed, and how many of left. This is a (poorly made) mock-up of the idea: