The jury was unable to reach consensus despite Campbell ordering the panel to reconvene.
McInerney was being tried for murder with a hate-crime enhancement in the shooting death of classmate Lawrence King in 2008.
McInerney, then 14, shot King twice in the back of the head in a classroom at E.O. Green Junior High School.
The prosecution alleged McInerney had planned to shoot King over unwanted sexual advances, and said that McInerney had white-supremacist leanings.
The defense contended McInerney had a violent upbringing in a rough household and that he snapped when King, who was gay, made repeated comments to McInerney.
McInerney, now 17, was tried as an adult.
The nine-woman, three-man jury panel said the last vote resulted in seven in favor of voluntary manslaughter and five for first- or second-degree murder.
The trial was moved to Los Angeles County due to media coverage.
The jury began deliberations last Friday.