Probably the most eloquent passage on the signaling model of education I’ve ever encountered, from Thomas Macaulay’s Government of India:

It is proposed
that for every vacancy in the civil service four candidates shall be named,
and the best candidate selected by examination. We conceive that, under
this system, the persons sent out will be young men above par, young men
superior either in talents or in diligence to the mass. It is said, I know,
that examinations in Latin, in Greek, and in mathematics, are no tests
of what men will prove to be in life. I am perfectly aware that they are
not infallible tests: but that they are tests I confidently maintain. Look
at every walk of life, at this House, at the other House, at the Bar, at
the Bench, at the Church, and see whether it be not true that those who
attain high distinction in the world were generally men who were distinguished
in their academic career. Indeed, Sir, this objection would prove far too
much even for those who use it. It would prove that there is no use at
all in education. Why should we put boys out of their way? Why should we
force a lad, who would much rather fly a kite or trundle a hoop, to learn
his Latin Grammar? Why should we keep a young man to his Thucydides or
his Laplace, when he would much rather be shooting? Education would be
mere useless torture, if, at two or three and twenty, a man who had neglected
his studies were exactly on a par with a man who had applied himself to
them, exactly as likely to perform all the offices of public life with
credit to himself and with advantage to society. [If this sounds like human capital theory, keep reading! -B.C.]  Whether the English system
of education be good or bad is not now the question. Perhaps I may think
that too much time is given to the ancient languages and to the abstract
sciences. But what then? Whatever be the languages, whatever be the sciences,
which it is, in any age or country, the fashion to teach, the persons who
become the greatest proficients in those languages and those sciences will
generally be the flower of the youth, the most acute, the most industrious,
the most ambitious of honourable distinctions.
If the Ptolemaic system
were taught at Cambridge instead of the Newtonian, the senior wrangler
would nevertheless be in general a superior man to the wooden spoon. If,
instead of learning Greek, we learned the Cherokee, the man who understood
the Cherokee best, who made the most correct and melodious Cherokee verses,
who comprehended most accurately the effect of the Cherokee particles,
would generally be a superior man to him who was destitute of these accomplishments.
If astrology were taught at our Universities, the young man who cast nativities
best would generally turn out a superior man. If alchymy were taught, the
young man who showed most activity in the pursuit of the philosopher’s
stone would generally turn out a superior man. [emphasis mine]

Me again: The only problem with Macaulay is his complacency.  Sure, education-of-whatever-kind is a useful signal when you’re trying to hire those “superior either in talents or in diligence to the mass.”  But when you evaluate a system of education, you can and should condemn those that emphasize dead languages, Ptolemy, astrology, and alchymy.