I have the same problem. I do get the occasional student to complete puzzles or even join a contest on CG, but those are rare. For high school, I recommend you use python turtle, for example on trinket.io or repl.it or just run locally on python with “import turtle”. Students get visual feedback from the drawings they can make with only few simple lines of code.
CG is useful for teaching, but not if students still need to learn basic coding such as loops and functions. In fact, they dont just need to learn those, but be able to comfortably use them to do anything meaningful on CG. That’s not realistic in high school unless you have a special kind of long running coding class.
Also with a CS class, there is a wide range of skill and knowledge among students. You’ll want to have something that even the “weakest” of students can progress on.