I have trained in the UK and in the USA.
Both can be variable, though my experience is that the UK is far more variable than the USA where the standards were very high indeed. A lot of stuff I saw here was absolutely atrocious.
But I know other pilots who reported lower standards in the USA.
You can, no doubt, find both examples, in both places.
As you can find across Europe; a big variation within the gold plated JAA-land...
BTW, while I have sympathy for the reasons for not sitting the exams in advance of flying, I don't think there is a clear cut case. A little while ago I "mentored" a very bright young lad. I went through the basics with him at our house, and we did some flights. He passed all his exams before even starting at a flying school, and I know he understood it just fine. But then he also had flying experience before he started training.