I'm delighted to hear that David enjoys our lessons—that was my sense of what was happening as well. It's gr8 to get positive feedback!
I'm hoping to get him hooked on reading interesting books in English as well as to provide opportunities for him to develop his expressive/spoken English. (He seems to understand so very much more than he's presently able to fluently express.) Of course, we'll work on written expression (composition) as well and grammar as needed.
I believe strongly that I can only set the stage for learners by providing appropriate material, instruction, motivation etc. Learning is a very personal process. I'm always amazed at how youngsters run with it and develop such confidence in using their English in a variety of settings and for many different purposes.
Enjoy observing his progress. Don't be too concerned with quantifying it or describing it. Have fun interacting with him in English when he shows an interest.