Why do so many, like many immigrants, start from nothing and end up very successful if it was just a dice roll? I mean, there's always that factor but it's certainly not everything.
“Most” and “upper middle class” tells me you’re probably making this up whole cloth. “Most” Americans don’t make it to the upper middle class.
Most of the immigrants I know spent a lot of time or money or both either personally or by their parents to get here. At least recebtly even the ones who left everything behind to start here with nothing at least had some talent at getting things done in beuracracy which is pretty useful.
I do not know if many American families can get access to the same resources for early education if they are not already from families that are economically affluent.