A jury of seven women and five men deliberated for about half an hour Wednesday.
Prosecutors had rested their case earlier in the day and defense attorneys declined to call any witnesses after two days of testimony.
The teen, who is not being identified because he is a juvenile, was one of five people charged in the beating death of 16-year-old Fenger High School student Derrion Albert during a mob brawl.
The teen's attorney said the boy hit Albert but that it didn't cause the other teen's death.
A pathologist said the single punch contributed to the student's death.