When Mia Stewart's swimming coach tells her to slow down, she doesn't listen.

"Whenever I'm swimming my coach tells me to go a bit slower, but I just have to go fast," the Year 6 Caringbah Public School (on Dharawal land) student says.

It's an attitude that has served her well.

The 12-year-old recently competed in the 50-metre freestyle multiclass event at the NSW Primary Schools Swimming Championships at Sydney Olympic Park.

There she clocked 41.90 seconds, a personal best that shaved 1.42 seconds off her previous time and left her just one spot shy of making the state squad for the national championship.

What makes that achievement remarkable is what most people don't see when Mia is in the pool.

Born with a one-in-a-million limb condition, Mia had pioneering surgery in the United States at age four that rotated her leg so her foot faces backwards, effectively turning her ankle into a functioning knee joint.

She returned to Australia with a prosthetic leg and a personality that has since refused every limitation put in front of her.

Mum Leila says the pool is a place where Mia can compete on her own terms.

Assisted by the School Sport Unit's Disability Inclusion team, multiclass athletes like Mia are supported at major events so they can focus on the thing that matters most to them: the race.

"Swimming is like a level playing field for her," Leila said. "She gives everything a go - she's always had that attitude."

It’s a perspective that extends well beyond the water. Mia dances, plays netball, and at her school swimming carnival she beat every able-bodied student in her age group. She is also school captain.

"I like talking," she says. "And being kind and a good friend."

Each year, Mia visits the kindergarten classes to talk about her leg, a ritual she now does alone having graduated from doing it alongside her mum. "I only get questions in the first three weeks," she says. "Then it's just: 'oh, there's Mia.'"

Leila says the family has never wrapped Mia in cotton wool, instead encouraging her to try everything.

"She's wiser than her years because of what she's been through, and she ends up being able to do things most other kids can't."

Caringbah Public School principal Jenny Morrison says while the school supports all of her endeavours, they have found that Mia is very much her own biggest advocate.

“She’s not shy in telling us what she needs but at the end of the day she needs very few adjustments,” Ms Morrison said.

“She does well socially and in sport and doesn’t shy away from a challenge. Mia is just a great role model who doesn’t expect special treatment.”