Seven-year-old Joanna Harris loves to tell stories, ones already written and ones she writes herself. When many of her classmates decided to rehash Disney movies during a school program, she wrote "Ocean Tale," a harrowing adventure featuring two mermaids almost captured by an evil fisherman. (Spoiler alert: Surfer Girl saves the day.)

Then the Paoli girl and her family spent July 4 visiting all 10 Once Upon a Nation storytelling benches around Independence Hall, where they learned the program was sponsoring a contest to celebrate its 10th anniversary. Joanna, of course, wanted to enter.

"This is what she does," said Joanna's mother, Jassamine Harris. "She loves to tell stories."

She tells good ones, too. She tackled the topic of her favorite "historic heroine" for the contest, writing about Helen Keller. She and the 12 other winning writers ages 7 to 12 will share their tales with the public Saturday. The young scribes will summon strangers to their benches by ringing a handbell, then will recite their stories from memory.

Joanna will tell the crowd why she chose Keller, talking about Keller's accomplishments and relating anecdotes a rising second-grader would find interesting - like the time Keller locked her mother in the pantry when she didn't like her baby sister, and when she acted like a "spoiled brat."

"I'm nervous," Joanna said during a recent visit to the Betsy Ross House, where she talked with veteran Once Upon a Nation storyteller Katie Frazer.

"Nervous is OK," Frazer said. "It just means you're doing something exciting."

Frazer calls her work "the best job in the world." The nonprofit Historic Philadelphia created the storytelling benches program in Philadelphia and Valley Forge in 2005. Through the 2014 summer season, more than 1.5 million visitors representing 50 states and more than 75 countries have gathered at the benches to hear free stories of history's lesser-known heroes.

"Less Benjamin Franklin and Thomas Jefferson, more about people you haven't heard of but who are remarkable," said Sandy Mackenzie Lloyd, a historian for Historic Philadelphia. "I look for stories where a person has to make a big decision, how they handled change, what they did to affect change. I want stories about the past that pack in emotion and have relevance in today's world. I want people to leave thinking, 'I learned something today' and 'I've had an experience like that.' "

Case in point: the story of Esther De Berdt Reed, being told this summer at the Betsy Ross House. Reed, English by birth, moved to Philadelphia just before the American Revolution began. She chose to stand up for her new country, writing a call-to-action pamphlet addressed to women. In 1780, Reed organized the first successful fund-raiser for the Continental Army, raising a whopping $300,000. Gen. George Washington told her that cash would be best spent on shirts for his soldiers, so Reed and other local women hand-sewed more than 2,000 shirts. Because they were women, they couldn't sign the Declaration of Independence. But they could stitch their names into every shirt they made.

Mackenzie Lloyd also wants the stories to inspire young people by showing them "people can go out into the world and make a difference." She hopes the storytelling contest has the same effect.

Because there are 10 benches, Historic Philadelphia planned to choose 10 stories. But the entries were all so good the judges couldn't decide which to cut. So all 13 applicants were declared winners, a number much more appropriate, Mackenzie Lloyd said. There were 13 original colonies, thus 13 stars on the original flag. A replica of that flag marks each storytelling bench.

Most of the winners are from Philadelphia and nearby suburbs. One winner will fly in with her family from North Dakota. That 9-year-old history fan, who has posters of the U.S. Constitution and Taylor Swift on her bedroom walls, wrote about Betsy Ross.

There's no duplication in the group of heroes and heroines. There is creativity. One girl wrote about all Revolutionary War soldiers, a type of "everyday man as hero" story. Another wrote about Phillis Wheatley, one of the best-known poets of her time. Wheatley, captured in Africa when she was a child and brought to Boston to be sold, published her first poem in a local newspaper at age 12.

Choosing Keller as her heroine was easy for Joanna. She'd first heard Keller's story when she was in kindergarten. More recently, she read a book on Keller, part of the "Who Was. . .?" series. At the Betsy Ross House, Joanna shared most of her story with Frazer. At one point, she forgot what came next and her 4-year-old sister, Christabel, whispered the next line in her ear. Joanna then continued to the end. Frazer was impressed. She pointed out different ways Joanna could pull her audience deeper into her tale: When Joanna talks about a ringing dinner bell, she could mime doing just that. She could learn a bit of sign language to pass on to her listeners.

"It helps if people can see what you're saying as well as hear what you're saying," Frazer said. "You're already doing a good job telling them, so now get them excited."

Joanna took in Frazer's advice but acknowledged, again, that she was worried about performing in front of a crowd. Frazer reassured her.

"You wrote an awesome story," she said. "If you have a passion for telling stories and you show that to people, they will love your story."