I don't know about your family, but I would know if one of my kids went to see a doctor for any reason.
Some States have parental notification laws, and others do not, but all parents are supposed to (or should) know what the hell their kids are doing during office hours at least.....
We have a parental grapevine , of sorts, in my community. All or most parents watch out for everyones kids. We don't pay much attention to BS privacy laws when it comes to our kids, and that is a good thing.
Teachers, professionals and even the next door neighbors will pick up the phone and notify parents if they think it is important.
Making a doctors appointment during school hours will eventually lead to parental notification in most instances at some point in time by way of various methods..
That is what I meant.......
IMO, the circumstances you describe are far from universal in this day and age. I'd tend to think they were rare, more than common. IMO.