Thus it is still good advice to tell students to work hard and do well in school, rather than saying it's okay to be lazy and not pass exams because, well, "education is only correlated with employment prospects".
1. By entering the workforce as young as possible, total lifetimes earnings (and more importantly, savings) are maximized for a longer period of time.
2. If the individual has no aptitude (or desire) for higher education, then there is a very good chance they will neither get the credentials, nor the knowledge that comes with a high level education.
3. Even if they did manage to squeak by and, through sheer grit and determination and stubbornness, acquire the higher education - they might now slot themselves into a field of endeavor for which they are singularly not suited for - only to find 10 years after working some white collar position, that they really, really wished they had been in construction/electrician/blacksmith/what have you...
Frequently the path to maximizing total lifetime earnings, happiness, impact, and productivity is not through higher education. I think that there is a lot of observer bias on most of our part, because most of us have gone through at least some post-high school education and would to believe it generally offers value to those who do likewise.
I've got a least one friend who really should have never gotten his Computing Science degree. He is brilliant in ways that I'll never, ever, match - and should be building houses, not trying to work in IT - just not his gig.
On the flip side, i have a quite comfortable six figure income, and never completed university - I just have an aptitude for working in IT.
I really believe there is a correlation/causation problem with the "Higher educations leads to Higher Income" - the one exception being that a Yale/Stanford/Princeton/Harvard/MIT/Ivy League graduate probably raises the ceiling (and position opportunity) for candidates above what someone without those credentials would have. But now we're talking about the difference between making $150K/year as a mid level manager and $750K/year as a Sr. VP - not as relevant to the masses.
I did exactly that, out of high school into a warehouse job, then tech support, then software engineering, when I look at the cost of student loans, lost work, lost investment opportunities, I put the cost of my BA somewhere around $400,000.
There are definitely people who would be better off dropping out as early as possible and start working but that's a minority.
Even electricians and mechanics require tertiary education. (Otherwise, what does my brother training to be a mechanic mean when he says he's going to "class"?!)
Dropping education as early as possible might be a good idea if your aim is to work in a field where knowledge can be easily self taught. (Like IT or painting). Even then, a one year crash course I think would be quite helpful. I self-taught myself programming too, but I only learned about "unit-testing" in university. I guess you can argue I could learn that in my first job, but what if I want to, say, do a startup? ;)
>> I really believe there is a correlation/causation problem with the "Higher educations leads to Higher Income"
We're talking about higher education leads to higher chance of being employed.