The dominant narrative of college in the United States is that of a campus with tree-shaded quads, ivy-covered neo-Gothic buildings, and of course, young adults fresh out of high school. And while many of the nation's colleges spend much time, effort, and money every year recruiting a new cohort of high-school graduates to not stagnate in the future, they also must service a much larger—and growing—group of students: working adults looking to gain new skills and advance in their careers by earning a higher level degree.

Rather than solely compete for the attention of the 3-million-plus students who graduate from high-school each year, college leaders should aim to satisfy the demand for learning among adults. The market opportunity is staggering. There are 15 million adults who have an associate's degree but no bachelor's. Another 35 million started college but left short of a degree. And those numbers don't include the nearly 7 million undergraduate and graduate students who are over the age of 24 and currently enrolled in higher education.

To attract this new majority of adult students, institutions can't simply repackage their offerings aimed at 18-to-22-year-olds. Nor can they serve these adults in ways that are convenient to colleges in terms of location and scheduling. Adults are pressed for time and often place-bound because of family and work obligations. They seek higher-education options that are fast, flexible, and provide outcomes that are relevant to their careers.

These new students don't want to spend time—or pay—for a buffet of options when all they might need is an entrĂ©e at a particular point in their lives. The problem is that many graduate programs are lengthy and force students to fulfill admissions requirements or curricular obligations that are not necessary for what they need right now in the job market.

This is one reason that the number of students enrolled in online education is on the rise at a time when overall enrollment in traditional higher education continues to decline. More than 6.3 million students took at least one online class in 2016, about 32 percent of all college students—up from 26 percent in 2012.

But online education will only stay on that growth path if schools continue to evolve in how they deliver digital learning.

First, rather than offer a patchwork of academic programs, colleges and universities must focus on fields that demand continuous upskilling, such as business, nursing, and education, as well as emerging fields where employers report they have difficulty finding skilled workers. The U.S. has 6 million unfilled jobs—1 million in the health-care sector alone—the most since the Labor Department started keeping track a decade ago. Most of these jobs go unfilled because applicants lack the required degree or needed skills.

Second, the structure of online degree programs for adults should stop following that of the traditional, campus based programs. In other words, they shouldn't have the same admissions requirements, start dates, and schedules. Today's adult students are more discerning and colleges can't expect to continue to serve up a one-size-fits-all experience. Online programs will need to be more differentiated in the future in order to succeed in an increasingly competitive and fragmented market.

Third, colleges need to rethink their legacy credentials. Enrollment in some master's programs is flat or declining. Even the venerable M.B.A. is falling on hard times. At the same time, trust in traditional degrees is deteriorating as employers increasingly question the readiness of graduates to navigate the modern workplace and economy. The time has come for institutions to design new signaling devices that their graduates are prepared for the workforce, such as microdegrees and stackable credentials.

The adult market represents a vast untapped market for colleges and universities, especially since the number of traditional-age college students is expected to drop substantially at the end of next decade. At the same time, the world of work is undergoing massive change, with the skills needed to keep up in any job changing at an ever faster pace. Education will be key to competing in this new economy, and those institutions that serve this new generation of students will be the ones who survive and thrive in the decade ahead.