During the academy's selective admissions, size is considered more than riding experience. The school prefers riders weigh less than 112 pounds and body fat expectations are far more rigid than other athletes, on par with the lowest percentage of body fat necessary to even survive.
"Your typical male jockey has a body fat percentage that ranges between three and seven," McCarron said. "The girls are between eight and 12."
Compare that to body fat percentages for the average American, which is around 18 percent for men and 25 percent for women.
Reill is a gifted rider and has a slim build but, she said, she still struggles to meet the weight requirements.
"I've stopped eating as much chocolate as I used to," she said. "And just trying not to go over 1,500 calories a day."
It's that kind of pressure that can be dangerous.
"Some jockeys would order a $20 steak and 20 minutes later go into the bathroom and throw it up," Yetter said. "They call it 'flipping.'"
'Flipping' in this world is slang for bulimic behavior.
"Unfortunately, bulimia is a pretty prevalent problem amongst jockeys and taking diuretics ...," McCarron said. "It's challenging."
Jockeys will risk their health and even their lives for a shot at professional racing. It's possibly the most dangerous professional sport in the country.
"Since 1940, at least two jockeys a year … are paralyzed," McCarron said. "So it's a lot more dangerous than NASCAR or parachuting or skydiving."
There are 48 accidents each week involving jockeys, according to the Jockey's Guild, which represents thoroughbred horse racing and U.S. professional quarter horse racing jockeys.
While her mother worries about her daughter's safety, Yetter said she doesn't let the potential danger bother her.
"I fell off and had a bad concussion last summer," she said. "[But], you know, 'Get back on the horse.' You don't let it faze you."
When "Nightline" visited the school again a few months after seeing Chase Roberts' first ride, he had fallen off and injured his knee, sidelining him for a month.
"I don't want to give it up," he said. "I couldn't wait to get back on the horse that knocked me off."
The burning desire is there, but their chances of making millions while racing horses are slim. Jockeys get 10 percent of the earnings, but only if they win.
"Money doesn't really ever cross my mind," Yetter said. "Honestly, I would be happy sitting on a plot of land in a trailer and having horses around me and riding on the track every day. I would be totally content with that."
They are all here for different reasons. It's adrenaline for some. It's money for others. For most, it's nothing more than the simple love of horses,
"When you're on that horse, they're running for you," Yetter said. "You can feel that. I love it. I'm 19 years old, and I'm living my dream."