Samantha qualified for international elite status in 2004 and placed second at the Junior Olympic National Championships. She qualified to the Visa Championships, where she finished 8th all-around and became the youngest junior national team member at age 12.

She improved her national standing in 2005, placing seventh all-around, second on floor and first on vault at the Visa Championships. Samantha was chosen for an international assignment in Mexico shortly after Nationals, winning the all-around, vault and floor titles.

Samantha shined at the 2006 U.S. Classic, finishing second all-around and winning vault and floor over fellow powerhouse Shawn Johnson. Samantha also placed second on beam. Her performance at the U.S. Classic made her a favorite to challenge for the junior national title. She performed with veteran-like poise to finish third all-around, second on vault and third on bars. A week after Nationals, Samantha traveled to Quebec, Canada for the Junior Pan American Championshps, where she won floor and placed second on vault.

Samantha has a busy gym schedule approaching 30 hours per week, but in her free time, she enjoys shopping, movies and hanging out on the family boat.

She was a member of the gold medal-winning U.S. team at the 2007 World Artistic Gymnastics Championships and the 2007 Pan American Games.

In March 2008, she competed at the American Cup. She placed 3rd in the all-around competition, behind teammates Nastia Liukin and Shawn Johnson.

After a solid performance at the 2008 U.S. National Championships, Peszek continued to prove her worth to the U.S. team at the Olympic Trials. At the conclusion of the meet, when she was invited to the final Olympic selection camp, most experts, including NBC's analysts, predicted she would be selected for the team. Indeed, she was selected on July 19, 2008 at the conclusion of the selection camp in New Waverly, Texas. Along with Peszek, Shawn Johnson, Nastia Liukin, Chellsie Memmel, Alicia Sacramone, and Bridget Sloan were also selected for the team.

She has high-difficulty skills such as a standing tucked full to immediate back pike (beam) and double twisting double (floor), but her gymnastics suffers greatly in the execution and presentation department.

During the 2008 Summer Olympics, Peszek was injured during warm-ups just minutes before the women's qualifier and was restricted to the Uneven Bars. She was the second gymnast to be injured on the 2008 Women's gymnastics Olympic team, the other being Chellsie Memmel.