I know I've mentioned this before but my brother managed to do a full JAR PPL, in Scotland , in Autumn......in 2 weeks. I accept that he had done some flying with me and is a pretty talented pilot but it is do-able in a very short space of time IF you have the determination, motivation (and money!) and you have a schools and instructor who is on-board. For my brother that meant one plane, one instructor all day every day.
Now I'm not encouraging people to go flying in unsuitable weather (becaese as an ATCO I end up picking up the pieces!!) but I do believe that too many instructors are too "whimpy" when it comes to going flying in "marginal" weather. I know there are implications for what the student will get out of a lesson when its pretty murky, and if its an early lesson when a good horizon is needed then fine cancel...but how many of you out there have been flying when its been pretty murky; I know I have many times, and I think it is good experience for student pilots to experience the problems of such conditions with the relative safety of an instructor on board.