Britney was cast in “The All-New Mickey Mouse Club” alongside future ex-boyfriend Justin Timberlake and rival Christina Aguilera. But before that, she was a child champion on “Star Search” (watch video).
She would go on to star in “Crossroads.”
Like Spears, Justin competed on “Star Search” (as Justin Randall) but lost in his first head-to-head. He would become one of many stars to break out from Disney’s reboot of “The All-New Mickey Mouse Club” (watch video).
He would go on to star in “The Social Network,” “Friends With Benefits,” and “Trolls.”
Aguilera’s powerhouse vocals were evident even when she was a young girl. She starred alongside Spears and Timberlake in the final two seasons of “The All-New Mickey Mouse Club” (watch video).
She would go on to star in “Burlesque” and “The Voice.”
Gosling sang and danced in choreographed routines and coordinating outfits alongside J.C. Chasez and Justin Timberlake — whom he actually lived with for a short time (watch video).
He would go on to star in “The Notebook,” “Drive,” and “La La Land.”
She would go on to star in “Felicity” and “The Americans.”
Back when she still went by Emily Stone, she competed on a show called “In Search of the Next Partridge Family.” She actually won the role of Laurie Partridge, but the “Next Partridge Family” never got made (watch video).
She would go to star in “The Help,” “Aloha,” and “La La Land.”
Another powerhouse singer, Nicole Scherzinger, was a standout from the start on the WB series Popstars (watch video).
She would go on to become lead singer of the group, Eden’s Crush, as well as the Pussycat Dolls. She voices Sina in “Moana.”
Taryn auditioned on the same show as Scherzinger, but didn’t make it nearly as far (watch video skip to 3:45).
She would go on to star in “Crossroads” (opposite Britney Spears) and “Orange is the New Black.”
Henderson auditioned for Season 2 of “Popstars,” where judges criticized him for being too Timberlake-like, right down to the frosted tips. He won a spot in the short-lived band, Scene 23 (watch video).
He would go on to star in “Desperate Housewives” and “Dallas.”
DaCosta initially wanted to pursue a career in modeling, finishing as runner up to Eva Marcille on Season 3 of “America’s Next Top Model.” She’s arguably the most famous alumnus from the long-running show (watch video).
She would go on to star in “All My Children” and “Chicago Med.”
Katharine was also a runner-up in her reality competition. She finished second to Taylor Hicks on Season 5 of “American Idol.” Her performance of “Somewhere Over the Rainbow” is considered one of “Idol’s” finest (watch video).
She would go on to star in “Smash” and “Scorpion.”
During the height of “American Idol’s” popularity, there was a spinoff show called “American Juniors” featuring talented young singers. Lucy Hale auditioned and won a spot in the final group. She has unexpectedly good vocals (watch video).
She would go on to to star in “Pretty Little Liars.”
Hale’s “PLL” costar Parrish also auditioned for “Star Search.” She attempted a difficult song, “On My Own” from “Les Miserables,” which didn’t win over the judges (watch video).
She would go on to star in “Pretty Little Liars.”
Chung was a member of “The Real World: San Diego” (2004), and one the few Asian-Americans ever on show.
She would go on to star in “Sucker Punch,” “Big Hero 6,” and as Mulan in “Once Upon a Time.”
Chung isn’t the “Real World/Road Rules” alum who made it in Hollywood. In 2003, he was cast in “Road Rules: Semester at Sea” and later in the seventh season of the “Real World/Road Rules Challenge.”
He would go on to star in “Grimm.”
Jennifer Hudson was shockingly eliminated from Season 3 of “American Idol” in seventh place (Fantasia Barrino would win that season). Her powerful voice — showcased in this version of “Circle of Life” — would lead her to an Oscar-winning turn in “Dreamgirls” (watch video).
She would go on to star in “Dreamgirls,” “Sex & the City 2,” and “The Secret Life of Bees.”
The fearless Knoxville performed many dangerous and downright dumb stunts on MTV’s “Jackass.” The series would spawn several movies (watch video warning: profanity).
He would go on to appear in “The Dukes of Hazzard” and “The Ringer.”
Leakes’ over-the-top personality and larger-than-life living landed her a spot on “The Real Housewives of Atlanta.” She eventually departed the show to pursue and acting career, but will always be remembered for bringing drama for six seasons (watch video).
She would go on to star in “The New Normal” and “Glee.”
Stevens is another actress you probably didn’t know has a great singing voice. She was a finalist on Season 9 of “American Idol” (watch video).
She would go on to star in “Faking It.”
Julianne was a professional dancer on “Dancing With the Stars,” winning back-to-back Mirror Ball Trophies with Apolo Anton Ohno and Helio Castroneves. She would depart the show to pursue and acting career, but returned as a judge (watch video).
She would go on to star in “Footloose,” “Rock of Ages,” and “Safe Haven.”
Before she was a small-screen cheerleader, Morris put her solo dancing skills to the test on “So You Think You Can Dance” (watch video).
She would go on to star in “Glee.”