The signaling view of college holds that graduates of elite colleges earn high average salaries not because of what they learned in school but rather because top colleges select for students who have highly valued traits, the two most important probably being high IQ and strong work ethic. Since in rich countries almost every smart, hard working person attends college not going to college sends a loud negative signal to potential employers. Elite colleges, of course, are fantastically expensive signaling devices.
Although I teach at an elite college I have a proposal for an alternate much less expensive and probably even more accurate signaling mechanism. An organization could have a one month program which only admits those who get a high score on the SATs or some other intelligence test. Then the entire program would consist of spending sixteen hours a day solving by hand simple addition and subtraction problems. The point of the program would be to show that its graduates can spend a huge amount of time doing extremely boring tasks with high accuracy. Graduating from the program would signal that you had both a high IQ and strong work ethic.
If the program had a reputation for graduating valuable employees then I suspect it would become desirable to many recent high school graduates. The challenge would be for the program to initially earn its reputation. Perhaps it could accomplish this by having some well-known backers, by giving big cash grants to its first few graduates or by promising the first few graduates attractive jobs such as at the SIAI.