With the difficulties new college graduates face repaying student-loan debt (now a cumulative $1 trillion in the United States) making daily headlines, it's only reasonable to ask if the cost of higher education is worth the potential reward of a bigger income. After all, two of the richest men in America, Mark Zuckerberg and Bill Gates, don't hold college degrees. Granted, both of them put in time at Harvard, but neither actually earned a diploma. You could, in fact, argue that they got their training on the job at Facebook and Microsoft, respectively, even if those are companies of their own founding.

But Wait! College Does Pay Off

Even as the cost of college has risen, though, so has the demand for college graduates – as have the economic penalties for not holding a four-year degree. Graduates with four-year degrees currently earn 98% more per hour than those without – the biggest wage gap in U.S. history, according to the Economic Policy Institute. The differential reflects a shift in the nature of the workplace: There are fewer positions involving physical labor like manufacturing and farm work and more knowledge-based jobs, like programming and marketing, where a bachelor's degree is required or preferred. (For more, read Are U.S. Colleges Still A Good Investment?)

Not convinced that making twice as much as the next (nondegreed) guy is enough evidence to weigh in favor of getting a bachelor's degree? Consider the study that MIT economist David Autor published in the journal Science that showed that, after all the costs associated with a college education were factored in, the holder of a degree over a lifetime of earnings came out $500,000 ahead. Not a bad deal for a four-year, five-figure investment. (Or, if you go to a private university, a six-figure investment: On average, a public university costs a total of $37,343; a private one, $121,930.)

On the flip side, high-school graduates are increasingly being penalized in a knowledge-based workforce. According to a Pew Research Center study looking at income inequality, high-school graduates have lost significant ground over the decades: Fifty years ago, the wage gap between high-school and college graduates who were full-time workers was $7,449 (as adjusted for inflation); now it is $17,500 for the Millennial generation, workers aged 25 to 32. Unsurprisingly, today's high-school grads are more than three times more likely to live in poverty than their predecessors.

Not All Degrees Are Equal

But what about holders of two-year associate degrees or people like Zuckerberg and Gates who have some college? Unfortunately, according to the Pew study, two-year-degree holders in the 25 to 32 age range hardly fare better than high-school graduates, with median earnings of a mere $2,000 more per year, for an annual average salary of $30,000.

Of those holding bachelor's degrees, the best earners were majors with a math or science bent, including biology, computer science, economics, engineering, finance, math and physics. However, the old standby, English, is not necessarily the dead-end major that it is often portrayed as being. English majors in various forms of digital communications can match their science peers' earnings. Marketing majors also excel in income.

The biggest winner of all? Chemical engineering majors, according to a study from the Hamilton Project at the Brookings Institute. On average, over a lifetime, college graduates earn $1.19 million; high-school graduates earn $580,000. Chemical engineering majors, however, will earn more than $2 million over the course of a career.

What On-the-Job Training Offers

But what about learning on the job: Isn't real-world experience preferable to an academic education anyway? On-the-job training is often free – or you may be paid. Even when you're not paid, it's a lot less expensive and usually takes less time than attending college. Unfortunately, many formal training program have fallen victim to corporate spending cuts, although there are still fields where hands-on training is available.

Industries in which guilds and unions dominate, such as construction trades like plumbing, carpentry and electrical, traditionally have had apprentice programs as a means to entering the business. All three major unions for electricians, for example, offer paid apprenticeships with on-the-job and classroom training. Similar is training for the growth fields of telecommunications installers and green-energy technicians. These are not casual commitments, though: All of these industries require at least 2,000 hours of on-the-job learning, with some requiring as many as 4,000 to 6,000.

In fact, the U.S. government has recently put a focus on high-tech apprenticeships as a fast track to a middle-class paycheck, with the Department of Labor pledging $100 million for grants to develop public-private apprenticeship programs in biotech, healthcare, information technology and high-tech manufacturing. Programs resulting from that funding should start appearing over the next few years.

Chefs and other kitchen staff often start their careers by learning and earning through a combination of hands-on training and classroom work. Although culinary school is an option, it is not a requirement. The American Culinary Federation offers formal, multiyear apprenticeships, while some vocational training programs place students in internships.

If working with your hands isn't for you, your best bet for on-the-job training for white-collar work is sales. Real-estate brokerages and telephone-sales operations typically offer real-world training. (See also Financial Careers Without A College Degree.)

Probably the most extreme form of on-the-job training is entrepreneurship, where starting your own business sends you to the School of Hard Knocks as you figure out how to manage employees, cash flow and inventory while simultaneously marketing your new business and negotiating with suppliers and customers.

The Bottom Line

Measured by statistics, the decision to get a four-year degree is a no-brainer. Even if getting a diploma means taking on substantial debt, research suggests that over the course of a career, you will still come out way ahead financially, even if you opt for the most expensive route, which is a private college. However, you are an individual – not a statistic – and where your interests, ambitions and aptitudes lie should ultimately determine your approach to higher education and whether your career path begins through academia or with real-world experience. It is possible to get very, very wealthy with only a high-school diploma; it's just a lot less likely. (See Investopedia's tutorial, All About Student Loans – especially Student Loans: Paying Off Your Debt Faster – if you decide to go the college route. Or find out How To Ask Your Employer To Fund Your Education.)