This is (anecdotally) not true for families in the highest income decile (in California). Kids are pushed harder to learn things earlier than when I was growing up. For example, nearly all of my kid's classmates could read before they started kindergarten. All could do basic arithmetic. Now that he's in first grade, most can read chapter books and have a grasp of multiplication. My mom pushed me hard to get me ahead of my peers, but I didn't hit those milestones until a year later. The standards and expectations are extremely high now because it's never been harder to get a spot at a top 20 university—perhaps because a top 20 school is the best chance you can get to maintain your living standards.