ABC News' Rich McHugh reports:

Sarah Thomas is on track to make history.

The married mother of three and self-described tomboy is poised to become the first full-time female referee for the NFL.

After nearly 16 years of officiating grade school, high school and college football games, Thomas, 39, was discovered by a scout for the NFL.

Sarah Thomas Ready for NFL's Call

Gerald Austin, a retired NFL official, recalled his conversation with the scout.

"He called me one day and said, 'I have an official that I think you need to look at,'" he said. "I said, 'OK, Joe, what's his name?' And he says, 'His name is Sarah.' I said, 'Sarah?' He said, 'Yeah, he's a she.'"

Thomas, a Mississippi native, is now one of 21 finalists in the NFL officiating development program. She's a top contender for the next available slot, meaning she could shatter the glass ceiling and become the league's first permanent female game official.

"I'm excited if it was to become a reality," Thomas told ABC News. "[But] just being here and part of the development program is exciting enough."

Although Thomas is breaking barriers as a female, she started her career in football through a male, her brother, with whom she attended a meeting for aspiring football game officials in the early 1990s.

"I got involved in officiating football because I was intrigued when these guys took it seriously," she said of that first meeting with her brother at the Pass Point [Miss.] High School Football Association. "But then I was more challenged at, 'Hey, I really don't know the game of football,' and, being a competitor, I really wanted to see, 'Hey, what's in store with this?'"

Thomas went on to become the first female to officiate in a Division 1-A High School football game in Mississippi and then began officiating at the college level in 2007.

"When I got started in this 17 years ago, I had no idea that there weren't any females officiating," Thomas said. "I never set out to become the first female official in the NFL."

"I'm just glad to be an official, wherever that may be, and just want to do the best job I can do," she said.

Thomas says that despite being a woman in the male-dominated sport of football, she does not feel like her gender slows her down or inhibits her opportunities.

"I don't feel that it's been harder for me because I'm a female," she said. "I think that we are just out here working as officials. … I think just on our credentials, just as officials, I think that's what moves us along, not because of our gender or our race."

Off the field, Thomas works as a pharmaceutical representative. She is also a mom to two sons, ages 12 and 9, and a 7-month-old daughter.

"I could not do this without the support of my husband and my kids," Thomas said. "It [refereeing] has been a part of my children's lives ever since they've been here, so this is just what mom does."