A bit off the topic, but . . I remember my grandmother expressing surprise and dismay that any of us youngsters would lay out in the sun to get a tan. When she grew up, whites were whites, and glad of it. It wouldn't have occurred to them at that time to want their skin to be darker . . if fact, the opposite. Grandma would wear long-sleeved shirts, a hat and bandanna around her neck to protect from sun exposure . . not, as would occur today, due to health concerns, but to preserve her "whiteness". My parents didn't lay out in the sun unless we were at the beach, but they didn't sweat getting tanned (or burned), and then generations after that have sought the tan as a way to look more attractive.
As for the "dumbing down" of schools: As a teen, I heard that college entrance exams (SAT, ACT) peaked in the early 60's and gradually declined from there. Maybe, as you say, this was done to try to help minorities close the achievement gap (which, of course, didn't work). But, I can also think of some other reasons. First, the distractions of television. During the 50's, TV's were not such a mainstay of family entertainment. They were small, black-and-white, and there was probably only one set in the house (and you know that Dad or Mom was going to commandeer the set for propgrams they wanted but which were not necessarily what kids wanted to see). But by the 60's, the sets were improved, both larger and with color picture, and the family might own 2 or 3 of them. The sets were not only more attractive, but now kids could go off to a separate room and watch what they wanted. From there, the distractions just proliferated, but I think it started with TV.
Another possible factor was the reduced authority of parents as time went on, sometimes enabled by the parents themselves. My parents endured hardships as children and were deprived of luxuries. When they became parents, I think the intent was to provide their own children with toys and comforts that they did not have. You might call it "being indulgent", but my generation of kids definitely had more luxury items than our parents' or grandparents' generations did. These luxuries not only vied with reading and writing for our time and efforts, but I think my generation ("spoiled") started to think that we didn't need to obey our parents as much as earlier generations had obeyed theirs . . that we could decide for ourselves, and if we didn't want to focus so much on our education, that was our choice. In my case, my parents told me and my siblings, "Be a kid while you are a kid. Don't worry about working yet. Have fun. There will be plenty of time to work later." And, while I didn't let me grades slack for long, there was a time in my early teens when I did not care about school and instead focused upon having fun.
Now, compare that attitude with the attitudes of parents and children today in copuntries that surpass Americans in educational achievement. In many parts of the world, education is a privilege to be thankful for and to not squander. Getting high marks is of paramount importance to one's future, and the kids feel great stress to do well and to be amongst the select group whose lives will then be much more comfortable. Meanwhile, in U.S., the goal is to allow every child into college, regardless of abilities and ambition level, and schools are pressed to adapt to the less-qualified and less willing to work at it.
Again, sorry for length of this . . .