(MONEY Magazine) – Rumor has it that hard work alone no longer guarantees a steady climb up the corporate ladder. It probably never did. Still, after a decade of corporate cost cutting and consolidation, the opportunity for promotions clearly has shrunk at most sizable companies. As a consequence, now more than ever, you have to continue learning new skills to open new doors. Generally, that means going back to school. The word is out. Nearly half of Americans ages 35 to 54 took an adult education class in 1995, up from just 17% in 1984.

If you're interested in staying in your current career but lack some key skills to get ahead, consider taking a certificate program at a local college. This education will make you a more valuable employee. Certificate programs, which provide specialized training for a specific subject, are particularly useful in industries where the technology--and therefore the required skills--are changing quickly. For example, an $18,000 medical secretary who wants to become a $49,000 physician's assistant will need certificate training. Such a two-year program would cost around $12,000 at a public college--obviously a good investment. "It used to be that certificate programs were offered just in engineering and medical sciences," says Richard Koonce, author of Career Power! (Amacom, $17.95). "But now there are certificates to improve job skills in almost every field, from computer programmers to aircraft mechanics."

More than 500 colleges and universities offer certificate programs on a part-time basis, so you can continue to earn while you learn. Figure on spending anywhere from $500 to $8,500 for a one-year, part-time program, depending on the number of courses you need for the credit. You can save a bundle if the certificate program you need is offered by a professional group. The Public Relations Society of America, for example, charges members $275 for its program. A similar curriculum could cost you $1,000 or more on a college campus. You may even be able to get a certificate in your pajamas via your home computer, but the cost can be steep. New York University, for example, lets part-timers obtain 20 computer-related certificates, from systems development to networking technologies. Cost: $8,500.

You should ask whether your boss will pick up some of the tab. "Many firms now provide up to 100% tuition reimbursement for work-related courses," says Joyce Schwarz, author of Successful Recareering (Career Press, $12.95). Large corporations increasingly make deals with nearby colleges to offer employees classes at significant discounts.

If you decide to change careers altogether and become a professional, you'll probably need a graduate degree. Expect to pay anywhere from $12,000 to $35,000 or so for a two-year program at a private college. Fortunately, these diplomas should boost you into a much higher paying job. According to the Bureau of Labor Statistics, the 1996 median salary for all workers with master's degrees was $45,292, some 30% more than the $34,736 earned by those holding a bachelor's. For help handling the cost, check out the list of about 1,500 scholarships described in Daniel Cassidy's Worldwide Graduate Scholarship Directory (Career Press, $26.99).

Even if you enroll in a class or two today, you'll almost certainly need to take a brushup course or two in the future. After all, no matter what field you end up in, "change is inevitable," says Jan Slater, co-author of Managing Your Career in a Changing Workplace (Richard Chang Associates, $14.95).