The accident happened around 12:30 p.m. at Mariner's Landing Pier on the boardwalk.
Wildwood Police Capt. Robert Regalbuto said the ride was in motion at the time, and the girl fell from its upper half.
She was identified as Abiah Jones, of Pleasantville. She was with her classmates from Pleasant Tech Academy.
The popular amusement park was hosting its annual Education Extravaganza - a day the park is open and marketed for area students and educators.
The event is described as "a day of hands-on learning and interactive participation utilizing the beach and Morey's Piers amusements."
"I'd like to say how sorry we are for the incident that occurred here," said Will Morey, president and CEO of the Morey Organization, which has owned amusement parks at the Jersey shore since 1969. This was the first death of a patron in the history of the organization, he added.
A Wildwood police statement said the cause of the fall remains unknown.
The 156-foot-tall Ferris wheel is among rides at Morey's Mariner's Landing Pier. Both Morey's and police said the problem did not appear to be mechanical.
Morey said it appears Jones was alone in one of the car's passenger gondolas, which is secured with a double latch. The door of the car opens inward, making it difficult to climb out of, he said.
The girl's body was found in the passenger loading area of the ride on the boardwalk, leading authorities to believe she fell from near the top of the ride because that's the trajectory she would have followed as she fell, Morey said.
Police took photographs of various passenger carts on the Ferris wheel, part of which was covered in white sheets, and were looking for witnesses to the fall.
The Ferris wheel, which was built in 1985, most recently passed an inspection on March 17, according to the New Jersey Department of Community Affairs.
After closing the Ferris wheel and a few others nearby but keeping the rest of the park open throughout the afternoon, the amusement park's owners decided around 4 p.m. to close the entire park for the remainder of the night. It reopened Saturday morning.
Some information from The Associated Press