The following is an exclusive excerpt from my upcoming book PURPOSEFUL: Are You a Manager or a Movement Starter? available on 5/22/18 from Portfolio, an imprint of Penguin Random House.

Research has demonstrated for years that high expectations have the power to improve performance. Experts call this phenomenon the Pygmalion Effect. Named after a sculptor in a Greek myth who fell in love with a statue he carved, the Pygmalion Effect occurs when an authority figure’s positive expectations lead to the improved performance of another person.

The effect was first demonstrated in 1966 by Harvard researcher Robert Rosenthal. He told teachers which of their students (about 20 percent) would be intellectual “bloomers,” saying those students’ results on a test suggested they would have surprising gains in IQ over the next eight months. The teachers were not told that the students on that list were actually selected at random. Eight months later, they retested the IQs of the randomly selected students and found they had improved, especially as compared to a control group. The teachers’ high expectations of the students they were told were intellectual bloomers caused the teachers to change their own interactions with those students such that the students had more belief in themselves and their ability to improve, and therefore actually did improve. The effect has been demonstrated many times since then with people in a wide variety of situations, ranging from military recruits to corporate sales teams.

In 2015, Jack Zenger and Joseph Folkman, who run a leadership consultancy, looked at the performance and engagement of people who worked for managers who gave more high ratings on performance reviews to their teams versus those who consistently gave lower ratings. Even though both sets of managers felt they were setting high expectations for their teams, their teams’ results diverged dramatically. As Zenger and Folkman describe in Harvard Business Review, “The people who’d received more positive ratings felt lifted up and supported. And that vote of confidence made them more optimistic about future improvement. Conversely, subordinates rated by the consistently tougher managers were confused or discouraged— often both. They felt they were not valued or trusted, and that it was impossible to succeed.” The actual belief that leaders had in the people on their team became a self-fulfilling prophecy, leading the people who felt their managers believed in them to actually improve. This is not to suggest that managers should artificially inflate ratings for people on their teams but rather that managers who have confidence in their teams tend to build higher-performing teams.

WHEN YOU SET high expectations for people and then believe in them and support them to reach those expectations, they can soar far beyond what you (and even they) expect. And not only do people perform better when they feel trusted and supported, they also respect and trust their leaders more, too. I’ve seen this as a coxswain and at every company where I’ve worked, but the most profound example in my experience was when I was a schoolteacher myself, early in my career.

When I was in college, I taught during the summers in a program called Summerbridge, now part of a national collaborative called Breakthrough, which helps highly motivated, low-income middle school students get on the path to college. At Breakthrough, all of the teachers are high school or college students themselves. Nevertheless, they’re given full responsibility for curriculum development, classroom teaching, and mentorship to the amazing young people in the program. I was only seventeen when I started teaching there, and to be entrusted with so much responsibility at such a young age was incredibly empowering. Wanting to deserve that trust made me work even harder, so I threw everything I had into being the best teacher and mentor I could be, and to learning as much as I could from the people around me.

Most of the students in this program were going to be the first in their families to go to college, and they didn’t always have an easy road to get there. Many of them lived in areas rife with gang violence; often, they were being raised by grandparents or single parents, or by parents who didn’t speak English. Many had to care for younger siblings at home or work to support their families. Despite all that, or perhaps because of it, they were incredibly motivated— motivated enough to fill out a long and very challenging application with essays and teacher recommendations, which, if they were successful and accepted to the program, would require them to spend their entire summer in school. Instead of thinking about relaxing, they were preparing for six weeks of full-day classes, followed by two hours of homework each night.

And they were excited about it.

It was the first environment they had been a part of where it was cool to be smart, where they could bond with other kids who loved learning, and where they could connect with role models who were just a few years ahead of them, showing them that the journey they wanted to take was possible.

The magic of Breakthrough is the opportunity for true empowerment: the organization and the leadership set high expectations for both the students and the teachers in terms of the outcomes they believe can be achieved. And because those high expectations are made clear and the support to reach them is there, people feel trusted and almost always reach or exceed them. This is true for the Breakthrough middle school students, over 90 percent of whom go on to graduate from four-year colleges. And it is true of the student teachers, more than 70 percent of whom go on to careers in education. It was also true for me. I went on to teach high school and to found my own Breakthrough program in Pittsburgh, which is still running twenty-five years later and has helped thousands of young people become first-generation college graduates. Many of those students came back to teach in the program, and one—Sarah Bachner—even became the director of the program for several years. This is another reason why movements are so powerful—when strong enough, they can continue even after the original leader departs. Other people from within the movement will pick up the torch and keep running.

Breakthrough, started by the incredible Lois Loofbourrow in San Francisco, is now a national collaborative with twenty-four affiliate sites around the United States and one in Hong Kong. All together, Breakthrough has prepared many tens of thousands of first-generation college students over the past several decades. It is precisely this belief in the potential of people and the setting of high expectations for them that causes people to be so passionate about Breakthrough in return.

Excerpted from Purposeful: Are You a Manager or a Movement Starter? by Jennifer Dulski, in agreement with Portfolio, an imprint of Penguin Publishing Group, a division of Penguin Random House LLC. Copyright © Jennifer Dulski, 2018.