Sekmeth makes a good point here. Too many FTOs are reluctant to send students up in marginal weather conditions and that means that they never gain the experience that they really need.
As a result, the student learns what they need to pass an exam but when they're allowed off on their own as a qualified pilot they can find themselves operating in conditions that are legal but far worse than they ahve seen before.
Ideally, early nav would be done in good weather to learn techniques but later exercises conducted whenever it's legal so that experience can be gained.