And that says more about our teaching abilities than our learning capabilities.
It's not about abilities, but about approved methodologies. School isn't designed to advance learning for as many students as much as possible. It's designed to produce similarly-trained units which can be moved to the next stage of usefulness to those who went to expensive private schools for people in charge. Temp workers, soldiers, that sort of thing. No Child Left Behind — we will take them all to die in the desert.
Does that mean we should offer "Advanced Statistics for Sports Fans II" and "Advanced Statistics for Theatre-goers II", etc.?
If these classes can cover useful material and appeal to sufficient numbers to have asses in seats with heads above them learning? Yes.
Should we put max headcounts in classrooms? Or should we simply weed out those people who can't hack the lecture format?
There is clearly a need for educational institutions which are capable of teaching to the individual student. Their lack is a factor of the structure of our society. Though we now produce plenty for everyone, we insist that people whose output is no longer necessary (nor, apparently, desired) are useless and that there is something wrong with them. Yet, society exists to serve its members, and not the other way around. If society produces unwanted members, it is society which has failed, not those individuals. But if your basic welfare were not tied to your productivity, then many people who now are forced to scrap and scrape to survive might have the time to make a positive contribution — perhaps even in education. But this is a matter of priorities — When we have corporate bailouts but not student loan bailouts, and yet permit CEOs of companies receiving bailouts to pocket massive bonuses, we not only declare but prove what our government's function is — to provide opportunities for rich people to become richer at the expense of all others. If we cared about the future, we'd show more care for education. Not with unfunded mandates and leading from the stratosphere, as exemplified by NCLB, but with a system which permits more individual attention.
At what point should the education system start leaving children behind?
Since we have an abundance of most sorts of tradesmen (there is little point today in becoming an electrician or a plumber) the answer really ought to be only when it is impossible to raise their interest. I believe that different people have different capacities, but I also believe that most people are operating well below theirs. Investment in education pays many dividends. Who is well-paid by investment in war?