SAN FRANCISCO — A new educational institution, the coding boot camp, is quietly emerging as the vocational school for the digital age, devoted to creating software developers.

These boot camps reflect the start-up ethic: small for-profit enterprises that are fast (classes are two to four months), nimble (revising curriculum to meet industry needs) and unconcerned with SAT scores or diplomas. Most are expensive, but some accept a share of the graduates’ first-year earnings or a finder’s fee from employers as payment.

Most important, at a time when so many young people are underemployed, most graduates, especially those from highly selective boot camps, quickly find well-paying jobs. In a recent survey of 48 boot camps, Course Report, an online boot camp directory, found that three-quarters of graduates were employed, with raises averaging 44 percent from their pre-boot camp pay and an average salary of $76,000.

Enrolling 20 to 40 students at a time, many boot camps have venture capital backing; in May, Dev Bootcamp, which started here and expanded to New York and Chicago, was bought by Kaplan, the educational services company.