Calling it "one of the most-difficult decisions I have made in my life," Olympic champion
Making the U.S. team at 15, Ross was the youngest member of the "Fierce Five" that won the team gold at the 2012 London Olympics.
Now 19, she also has five world championship medals -- including a silver in the 2013 all-around -- on her resume.
"Having the opportunity to represent the U.S. through gymnastics has been an experience I will always cherish," she said.
Martha Karolyi, the national team coordinator, said: "Kyla not only was known for her work ethic and dedication, but also for her desire to reach perfection, which is an important component for a gymnast."
Her departure makes the powerhouse UCLA women's gymnastics team even better. Ross had previously delayed her enrollment at the school to try for the 2016 Rio de Janeiro Games.