@happygardening it should be clear that I'm focusing on something other than academic accomplishments as I'm emphasizing a timeframe well after formal schooling finishes. Anyway, IME academic accomplishments are only weakly correlated with income. My observation is that career results depend far more on self-discipline, emotional intelligence, resilience and luck, than do academic results. But I've also noticed that luck tends to be positively correlated with resilience and discipline; the more times you try, the more chances you have to get lucky while the more prepared you are, the more you can take advantage if you do get lucky.
Right now the state mandates that we spend about 1/6 of our lives in formal education and an increasing number of people are spending up to 1/4 of their lives in formal education. But most of those years come before adulthood.
Focusing on our adult lives, I don't believe that judgments passed much before age 35 have much value. I've known plenty of people who reached their late 20s with all the outward manifestations of early success and end up divorced and working in soul-killing, albeit lucrative, jobs. Conversely, I've known plenty of people who struggled with relationships and various penal forms of training in their 20s who emerged in stable relationships after finding someone special, and who were able to do what they genuinely enjoyed. There's just too much noise in the transition between education and the bulk of our adult lives.
As for "value-added", the top academic schools generally admit children who had the discipline to learn what they were told to learn. They then shed some of the less resilient ones along the way. Others leave these relatively high-pressured environments because they are less socially adaptable and, therefore, less happy. It should not be surprising that the survivors of this process are more disciplined, more resilient, and more socially adept than the average. How can you attribute how much of that is due to a school's teaching as opposed to the selection and survivorship biases?