I've found that with programming, people either follow along or they don't, and it becomes obvious which one is the case fairly quickly. The first type of person will ask you a question, and fully or partially understand the answer. The second type will ask a question, and then stare like a deer in headlights at the answer, so you explain a little more, and get the same reaction, explain a little more, and get the same reaction, and so on, until at some point you see that you're taking them deeper and deeper into a dark tunnel with no exit on the other side.
I hope your question gets more upvotes and responses as I'd like to hear others' experiences.