What is the one trait that makes for a great manager? You might be surprised

That is what I found in a study of a large multinational firm, covering 200,000 workers and 30,000 managers in 100 countries, and spanning over 10 years. What set top managers apart from their peers, more than any other factor, was their knack for reallocating people into just the right roles—or helping people make those moves themselves.

The job shifting was important for everybody. The employees ended up being more productive and earning higher pay in their new roles—and the positive effects for both company and employees lasted for years after the switch.

Finding the highfliers

To identify top managers, I looked for those who rose through the ranks of the company at a faster pace than their peers. Early promotion usually goes hand in hand with other markers of merit, such as salary growth and standout 360-degree performance ratings. In the end, about a quarter of all the managers were tagged as top performers.

Then I looked at how the two groups of bosses performed during manager rotations—a practice where leaders regularly move to different teams, usually every two years—to see how the top leaders distinguished themselves.

Here is how it worked. Let’s say two different teams of comparable workers have a regular boss (in other words, not a top manager). Then the managers rotate, and one of those two teams gets a top-performing leader while the other team gets another lesser chief. Since the two teams are otherwise the same, the manager would be responsible for any changes in performance.

The results were striking. For one thing, employees who had contact with a high-quality manager were much more likely to make a lateral move within the firm—about 40% more likely than other workers, within seven years of being assigned to a top manager. These weren’t trivial moves, either: They often involved large changes, such as moving between completely different roles at the company.

That leads to the next striking difference in performance. The workers who served under a top manager and changed jobs were much better paid and much more productive than other workers. Within seven years of contact with a top manager, these people earned about 13% more than workers with lower-performing managers. And their performance metrics—like sales per capita—were 16% higher than other workers’ numbers.

Can we really give the manager credit for all that? My analysis showed that changing jobs in itself explained about 64% of the workers’ pay increase. And, as we’ve seen, having a top manager made people much more likely to change jobs in the first place.

Spotting and encouraging

The fact that the effects lasted so long tells us even more. If a top manager were just a good coach or motivator, employees would show big gains while serving under the top manager, and the gains would fade once the high-performing leader left the scene. But worker mobility and pay rose steadily even after the manager departed.

Likewise, if the top manager were just a good teacher, their workers would likely improve in their current jobs—but they wouldn’t necessarily move on to very different roles and thrive there. As we’ve seen, though, that is exactly what happened.

In some cases, the top managers themselves moved people into new jobs. But top managers also inspired employees to seek out new roles on their own: Their employees were 9.7% more likely than other workers to complete a profile on an internal job-matching platform, and they were 50.5% more likely to take on short-term assignments outside their core teams.

Clearly, the managers had a knack for finding workers’ unrecognized strengths and aspirations, and steering them toward better-fitting roles. The data bear this out. Top managers devoted about 19% more time to one-on-one meetings with workers, for instance. What’s more, in interviews I conducted, workers described good managers as mentors who guided their career development with structured feedback, and who created opportunities aligned with employees’ skills and aspirations.

One worker told me that a manager recognized the worker’s interest in graphic design during a routine project presentation. So the manager assigned the worker to lead the design of part of a new campaign. After another worker expressed an interest in learning about digital marketing, the manager facilitated a cross-training program with the marketing function, enabling the employee to ultimately move into a new role that was a better fit.

Given all these results, the course of action is clear: Company leaders should measure and reward managers for developing talent through smart reassignments, not just team output. Likewise, companies should expect managers to spot people’s unique strengths and place them in better-fitting roles; that job shouldn’t be left to human resources. And companies should encourage managers and employees to remain agile by making it simpler to rotate into other parts of the company, even if just in the short term.

Putting workers in just the right spot is what top managers do best. Companies must recognize that strength and make the most of it.

Virginia Minni is an assistant professor of economics at the University of Chicago Booth School of Business. She can be reached at reports@wsj.com.