(FORTUNE Magazine) – Do people in your office seem less enthusiastic than they used to be? Do they come in late, or not at all, more often than they used to? Do they respond more slowly or more sloppily to direct requests? If you're a manager, you may be all too familiar with "warm-chair attrition," as consultants call it. More than 70% of U.S. employees are "disengaged," says a recent Gallup poll, meaning that they've mentally checked out of their current jobs and are just waiting for the job market to heat up so that they can go find another one. Part of the reason is that successive waves of layoffs have left survivors just plain tired. "But the problem isn't just overwork. It's that so many people are being worked to death doing stuff they already know how to do. They're not learning or growing," says Jeff Howard, a senior vice president at Boston-based Novations Group (www.novations.com), a consulting firm whose clients include heavyweights such as Microsoft, Pfizer, PepsiCo, and Wal-Mart. "As a manager, you can fix that. But first you have to understand that your No. 1 job is developing people--and that means all of your people."

Wait a minute. Who has time for that? Aren't managers already running as fast as they can? Absolutely, says Howard, and so they tend to rely on one or two "go to" people--or just do the extra work themselves--to get crucial projects done on time. "When managers tell us they don't have time to delegate important tasks to people who'll have to be coached through them, we say they don't have time not to," says Howard. "You have too much to do to depend on just yourself and a couple of stars. How much more could you get done if your entire team was running on all eight cylinders? How much more productive and less stressed out would you be?"

What often gets in the way is the notion many of us carry around in our heads that employees have certain fixed abilities, and we assign work accordingly. But according to Howard, most of our assumptions about other people's abilities just aren't valid: "Human beings are designed to learn new skills. We all do it from birth. In organizations the manager's role is to make it happen." How? First, make all your team members aware that they will be asked to master new challenges. Then, give them "stretch" assignments that require bigger or more complex skills. Finally, and throughout the process, give them specific feedback (good and bad) on how they're doing. Sounds straightforward enough, but what if an employee just doesn't step up to the plate? "In general, we find that people do," Howard says. "They don't want to do the same mind-numbing work over and over. They want to participate in change." He adds, "Using time pressure as a tool for developing people does take a tolerance for risk. But the greater risk is not doing it, and working your way into a corner that eventually will overwhelm you"--maybe even at the very moment when all those checked-out clock-watchers start heading for the exits.