I got a response from Codecademy acknowledging that the problem I experienced was on their end. They gave me some code that would let me get past that lesson, but it contained a variable that wasn’t mentioned in the lesson. That’s frustrating, and I don’t know that they’ve fixed it for everyone else yet. At least the response was fairly fast and friendly, with an explanation that they’ve been doing a lot of edits on the site lately. And what can I say—these exercises are free.
I should mention that each lesson at Codecademy is written by a different person, so they can be a little uneven. The overall quality is quite good, though. Still, that leaves me wondering if my trouble with the OO issues has anything to do with the author of the exercises or if I’m just getting in over my head now. Either way, I’m pressing on and intend to get through all of the lessons offered.