The U.S. economy has improved in recent years, however slowly. That has benefits for membership, meetings, and other ways people engage with associations. Back at the office, though, that growth can have a downside: People who once felt they had to stay put in their jobs for lack of better options are now more able to move on.

That’s just as true of the top of the org chart at nonprofits as anywhere else. According to recent research from the Bridgespan Group, 43 percent of C-suite jobs at nonprofits needed to be filled in the past two years. and nearly 25 percent of C-suite leaders say they plan to leave their current job in the next two years. Many of their replacements come from other nonprofits, according to three authors of an article on the study for the Stanford Social Innovation Review, arguing that nonprofitdom is facing a crisis of a “turnover treadmill at a time when the sector needs experienced, capable leaders more than ever.”

And if they get those leaders, they usually don’t get them internally—the study says that only 30 percent of senior roles in the past two years were filled with current staffers. The problem, as any small and midsize association staff knows, is that opportunities for upward movement can be scarce at such places. If you have ambitions toward the corner office and there’s no evidence that the CEO is planning to leave, a second-in-command gig can only become more frustrating over time. The study authors quote one nonprofit executive chafing against just such a flat hierarchy: “I haven’t even had the right experiences to move to the next level if I wanted to. I need to learn to manage people and to build my external networks.”

Yet opportunities to do that learning can be scarce too. The authors say that a main reason why leaders leave is lack of mentoring, where people take an active role in a staffer’s career growth. “We heard this from all stages of the leadership pipeline,” they write, “including CEOs, who said their boss, the board, failed to mentor them or, worse, made life more difficult by micromanaging.” Bottom line: If you’re not giving staffers opportunities to grow in their jobs, and asking them what kind of growth they want, they’re likely scanning the want ads.

Fixing that is easier said than done, of course. About a year ago, I discussed why training staff in leadership needs to involve more than just a seminar or two; often, there’s no direct connection between the training and the employee’s actual job, and little effort to help make that connection. Senior staffers can provide stretch assignments, which the SSIR authors recommend: Even at flatter nonprofits, “skill development can compensate for lack of upward trajectory. Stretch opportunities about in smaller organizations where a large number of responsibilities are divided among a small number of people.”

Well, yes and no. What looks like a “stretch opportunity” to a leader can be seen as “other duties as assigned” to a staffer who’s disinterested in the kind of work offered. People who want to get better at project management will only get so much out of helping out with marketing tasks; aspiring fundraisers don’t necessarily want to pitch in with meeting planning. They’ll do those things, of course, in the name of being a team player, but it likely won’t do much to reduce turnover.

Recently I’ve been speaking with association volunteer leaders about what’s helped them become successful and satisfied in their work. Two general themes rose up: The best leaders entered the work with a clear idea of what they wanted to accomplish, and they were directly asked by others in the organization not only to take part but how they wanted to do so. That sensibility applies just as much for staff members, I think: If you want to keep good people, it’s imperative to learn what they want to accomplish, and to find out more often than the dreaded annual performance review. You may not always be able to provide everything that staffer needs to grow, but just by being the kind of organization that asks you’ll distinguish yourself from the majority of organizations.

What do you do to retain your best employees and give them ways to expand their skills? Share your experiences in the comments.