Pine Bluff police chief Kelvin Sergeant said investigators thought the shooter was a 15-year-old man who was also a student at Watson Chapel Junior High.
The suspect was located in the neighborhood near the school and hid behind a house.
He was arrested and is currently being held at the youth center in Pine Bluff, authorities said. Formal charges have not yet been filed.
There is no motive for the shooting, Sergeant said, calling it an isolated incident. The school followed the active shooting protocol, sergeants said.
In a Facebook post, the school system said that students are safe and that schools are being closed.
Pine Bluff is about 45 miles south of Little Rock, the state capital.
Correction: This story has been updated with the correct age of the victim. The victim is 15 years old.