A weakness in the UK system was that the instructor (and flying school) got paid by the flying hour: I guess it is still the same. I recall doing extra ground school when I thought it sensible and the opportunity arose. However, I also recall that some students just glazed over and you were wasting your time.
Hear, hear. Paying instructors by the hour doesn't encourage good teaching practices/methods.
Most students I taught just treated the groundschool as an annoying hurdle to get out of the way. They didn't have time, nor the commitment for it. Most helicopter students are "cash rich time poor".
To be fair though, the JAA PPL exams are a joke. How is a knowledge of induced flow, bus bars and ICAO annexes going to help you when you get lost/the engine quits/the weather turns poor?
The FAA system is much better, one exam, covering a general level of detail in all subject areas.
There needs to be more emphasis on decision making, power-on forced landings, weather diversions/planning etc. in the PPL syllabus, and daft things like downwind quickstops should be removed.