PHOENIX -- A Cottonwood student is in the hospital with a possibly ruptured spleen after another boy punched him in the stomach Wednesday afternoon, authorities said.

Deputies found out about the assault after the victim's mother called the Yavapai County Sheriff's Office, saying her 13-year-old son had been attacked earlier in the day at the American Heritage Academy, according to spokesman Dwight D'Evelyn from the sheriff's office.

School officials told deputies that students and at least one staff member witnessed "a commotion" earlier that day, D'Evelyn said.

A 14-year-old boy was detained at the school until his mother took him home, D'Evelyn said. School officials told deputies the boy had punched the victim in the stomach without apparent provocation.

"The exact cause of the assault is still under investigation," D'Evelyn said.

The victim was treated at the Verde Valley Medical Center for his injuries, but was later airlifted to Phoenix Children's Hospital for the injured spleen, D'Evelyn said. He remained there Thursday under observation.

According to the sheriff's office, the 14-year-old boy was booked into the Prescott Juvenile Detention Center on charges of aggravated assault, disorderly conduct and disruption of school activities.