with bill weir. For 25 years, oprah winfrey ruled daytime television, with the power to instantly transform author into best seller or doctor into famous medical guru. But it was offscreen and in a... See More
with bill weir. For 25 years, oprah winfrey ruled daytime television, with the power to instantly transform author into best seller or doctor into famous medical guru. But it was offscreen and in a far away place she pursued her deepest dream of changing lives. She told abc's juju chang about the girls she thinks of as her own daughters, in this "nightline" exclusive. As a mother, as just a person who has been apart of your lives for the past four, five years, i never have been more proud. I think you all were -- you made me a really proud momma. Reporter: She may not have biological children, but thanks to the first graduates of the oprah winfrey leadership academy for girls, oprah says she now understands the trials and tribulations, as well as the joys of parenthood. Nice to see you! Reporter: All seen in the documentary, "the first graduating class." So, when they call you momma oprah, that's for sure. If you were there for more than ten minutes, they would call you sis juju. Reporter: If one of these girls calls you, you pick up the phone? Yeah, we're texting all the time. As a matter of fact, it just happened this morning and I was on the phone last night for an hour one of them trying to watch the debate. Like, okay, trying to watch the debate, but okay, I'll hear what you're saying. Yes. I think I've come into my mothering space in a way that was wholly, wholly, so unexpected. I just -- I -- I knew from the moment that I met these girls that I was going to fall in love with them and I did. Reporter: The maternal bonding began five years ago, as a leap of philanthropic faith, inspired by the venerable nelson mandela. What is the single life-changing trajectory-changing moment for me, was being exposed to a world of education that offered me a new insight into how I saw the world. So, I just wanted to do that for somebody else, that's all. Reporter: Out of thousands of applicants, oprah hand-picked 72 girls. Do you think I'm good enough to be selected to go to the school? I think that you are. Good enough. Reporter: Girls from shanty towns. 60 families living together. The house that I live in with my mom is a very small house. Reporter: Girls who experienced trauma and the hardships engrained in poverty. Girls a lot like a young oprah winfrey. At the time that I grew up in mississippi, it was very much like south africa. It was apartheid mississippi. It was. And segregated schools, no running water, no electricity. Which was just the way, you don't think, oh, gee, everybody else has it and I don't. That's just the way I grew up. It's amazing that I've come from that to my own ipad. Reporter: The girls and their families understood the life-altering guilt of education. You will be apart of the very first class of the open what win free -- Reporter: In a setting so luxurious, simplemenities were cause for celebration. One of the moments that i thought so captures the gap that you are trying to bridge with the girls is when they react to the plumbing. Ah, yeah, that is still one of my favorite moments. Reporter: Me, too. Talk about favorite things. They were most excited, of course, about the plumbing, because it means I can take a shower, I don't have to go and find buckets of water that is one or two kilometers away. I don't have to share a pump on a yard with 56 other people. I can have my own bed. I can have -- I can flush the toilet! Reporter: But there was also scan dam. When a female dorm adviser was charged with sexually molesting several girls, oprah fired her and other staffers. Oprah, talking about the sex abuse allegations rocking her beloved school for girls. Reporter: Instead of distancing herself, she flew to south africa to personally apologize to the students and their parents. You learn from your mistakes. You learn by doing. And if I had it to do over again, I probably wouldn't have done it this way. Certainly, I know enough now that I can help other people. Reporter: "Forbes" magazine estimates that the 58-year-old has devoted roughly $400 million of her fortune towards education. But still, some may wonder -- why is oprah investing in south africa when she should be investing -- I don't look at it as just an investment to south africa. It's a gift to the world. All of the girls are going to be in places all over the world. Wherever the future of the world decided, those girls will be sitting at the table. That's my great hope and desire for them. Reporter: But the truth is, she's invested heavily in the u.S., As well. 400 scholarship winners, the so-called sons of oprah paid tribute in the emotional highpoint of her 25-year run on the oprah show. Over 400 men. Reporter: The film follows the girls' epic journey from the poorest townships from south africa, all the way to graduation. There were many days during these past five years where I've asked myself, what were you thinking? What were you thinking, you could build a school? I was thinking about this day. I was thinking about this day with them walking in triumph across this stage in their white dresses. The class of 2011. Reporter: So, like any nervous mom sending kids off to college, six of them here in the u.S., Shopping for dorm furnishings with them left her feeling like an empty nester. The very first morning that the girls from the united states were here and we were all going to, I can't believe, I'm reaching over target and bed bath & beyond. But the morning we were all getting dressed to go shopping for their college dorms, I mean, I -- it's -- the moment it hit me. Reporter: It's been a journey, too, for oprah. Her cable network own has struggled. But recently, it's enjoyed a ratings uptick. At first, I was sort of bogged down and if you had asked me this three months ago, i probably would have had a different feeling about it, like, ah, it's so challenging. Now, I can see the light. I look at it as though I was climbing kilimanjaro and I was just, had my head to the ground and one foot in front of the other. Now, I can see the summit. Reporter: Isn't that nice? I can see the summit. Reporter: For "nightline," I'm juju chang in washington, d.C.
This transcript has been automatically generated and may not be 100% accurate.