We too have lower figures of ADHD than USA. But more than in France. (I think our figures are something like 5 % of kids between age 6-16, less in adults. Less than 2 % of them severe; meaning needing medication instead of just other supports.)
And we certainly are in the other end of spectrum than France in demanding and disciplining our kids. Only thing we do demand from our kids is rather high level of independence from early age. Our kids walk to school alone at age seven. At age eight they spend afternoons home alone etc. But other than that we tend to have very low expectations for our kids behaviour. We always aah and ooh to French or American well behaved and articulate children - and let our own grow total hillbillies and totally expect them to be total hellions and hope they just learn to behave in furnished rooms, say hi to others and look towards the people when they talk to them around the time they turn twenty. Most do. Okay, other thing we demand from our kids is high academical performance. But how they learn is mostly up to them, if they don't feel like working for school it's mostly okay to us, if they are smart enough to still learn.
But other than that we don't have high expectations. We certainly don't expect a child to sleep through night before they are two or three. If they want to eat just ketchup, macaroni and hamburger meat till they are five, we are okay with that. We start to consider if we would need to teach them a word 'no', when they turn two. We expect them to start to consider saying their first words before they turn three, but no one is concerned if toddler doesn't talk more than a word or two when they turn two. We consider it excessive if our kids under six have something else to do than free play more than four hours a week. Or if our first or second grader has more than four hours of school a day (with every class being 45 minutes and 15 minutes being free play outside before next class.) With third and fourth graders may have a day or two with five classes a day. Even our 13 to 16-year-olds have 30 hours of school at tops a week (with those 15 minute outside breaks after every class.) Our kids start kindergarten (mostly free play, not real academic goals other than writing your first name and knowing numbers to ten) at the fall of the year they turn six. Many postpone by year their boys who have born at fall and would be youngest of the class. Kids are expected to have learned to read at spring of second grade, most of course learn first grade and many even before. But parents are concerned if their four- or five-year-old learns to read and worry the child's childhood may be endangered.
So, the answer why we too have lower ADHD figures than USA is certainly not the structure and discipline. Genetics could be the factor. Maybe also the opposite than in France. Kids with higher activity level and less ability to concentrate can still keep up with others, when not much work or sitting or things like that is demanded.
... this is, as Witz said, a conversation starter. Period. 
