The incident was caught on surveillance video on Dec. 28. Officials said one suspect walked in and grabbed some beer at the Circle K store on the 12000 block of Knott Street.
As the clerk questioned the suspect's age, a second suspect walked in to the store. Both suspects started attacking the clerk. They then attacked a customer who tried to intervene.
Authorities said one suspect, a 16-year-old man, turned himself in because of media coverage of the crime. The second suspect, a 17-year-old Westminster man, was arrested at school at about 10:30 a.m. Tuesday.
Anyone with information was asked to call the Garden Grove Police Department at (714) 741-5704.