I haven't done any classroom sessions at all - just read the books (AFE/Pratt), then had a go at AirQuiz
This is exactly how I study Riverrock. I study using Pratt, some added textbooks from works library and informal chats to my FI and other pilot friends within the club and outside. I also use the PPL Perfector for practise papers. This way certainly works for me. You mention that you are learning in a club environment rather than a "school" perhaps this more "laid back unofficial" approach which both our clubs have to ground study is part and parcel of learning at a club. Personally I think this is a great way to learn...formal classroom teaching would be far too much like going back to school!!
I suppose if the 100hrs was made more formal, the way to capture it would be in a logbook much like the flying hours..... but if it were to be brought in it would need to be for brand new students - not those of us who are nearing the end of our training!! God knows how I would capture all my hours spent at a desk with a textbook!
