According to the U.S. Department of Education (USED), while 75 percent of the fastest-growing careers require post-high school education and training, more than half of middle class students who start college fail to earn a bachelor’s degree within six to eight years.

As CNN Money observes, this low graduation rate means it’s more difficult for young adults to remain in the middle class or raise themselves to a higher economic level without a college degree. Not much is known, however, about what happens to students from middle class families since most research has focused on how low-income students can get to college.

Sandy Baum, a research professor at George Washington University, said, “It’s startling. We get people to college, but they don’t finish. The middle class gets lost in the shuffle.”

The USED statistics show that only 40 percent of 2004 high school seniors who entered college and whose families earned between $46,000 and $99,000 had earned bachelor’s degrees by 2012. Meanwhile, 63 percent of high-income students and 20 percent of lower-income students graduated from college.

Additionally, only 45 percent of students who started college in 2003 and whose families earned between $60,000 and $92,000 had earned a bachelor’s degree by 2009.

Baum states that the longer students are in school, the less likely they are to graduate. Full-time students are also more likely to earn a bachelor’s degree, as evidenced by the fact that 63 percent of middle class students who started college in 2003—and were full-time students—earned their degrees by 2009.

A bachelor’s degree is still the best assurance of a higher income, according to Federal Reserve Bank of New York economists Jaison Abel and Richard Deitz.

The economists note that “even with the recent decline in wages, those with a bachelor’s degree have, on average, continued to enjoy a 75 percent wage premium, while those with an associate’s degree still earn over 20 percent more than high school graduates.”

Abel and Deitz observe that engineering majors in college can expect a 21 percent return on their bachelor’s degrees, while students majoring in math and computers can expect an 18 percent return, and business majors a 17 percent return.

Radio show host and finance expert Clark Howard also recently cited the “Top 20 Best-Paying College Majors” and their starting salaries, courtesy of Michigan University’s Recruiting Trends 2014-2015 report:

Electrical Engineering – $57,030
Computer Engineering – $56,576
Mechanical Engineering – $56,055
Software Design – $54,183
Computer Programming – $54,065
Chemical Engineering – $53,622
Computer Science – $52,237
Civil Engineering – $51,622
Mathematics (includes applied) – $47,952
Construction – $45,591
Supply Chain – $45,508
Finance – $44,699
Accounting – $44,525
Nursing – $43,481
Chemistry – $43,344
Human Resources – $42,495
Marketing – $41,481
Economics – $41,118
Humanities & Liberal Arts – $39,162
Agricultural Sciences – $38,854

According to MSU economist and College Employment Research Institute director Phil Gardner, “Engineering always tops the average starting salary list. While averages fluctuate because of economic conditions, engineering salaries have not been exceeded by other disciplines going back 65 years.”