Deer Valley and Antioch high schools were targeted in the threats, as was Black Diamond Middle School.
Deer Valley High received threats every day this week, and classes were repeatedly disrupted as students and staff were evacuated.
This morning, three threats were called in. The first, at 7:43 a.m., came from someone who stated there was a bomb at Black Diamond Middle School, police said.
The other two calls, made at 9:39 a.m. and 10:50 a.m., focused on Deer Valley High.
Antioch High School was the target of a bomb threat on Wednesday.
All of the threats were determined to be hoaxes.
Detectives investigating the threats arrested the juvenile, who has admitted to making the calls, according to police.
Anyone with information on the case is asked to call Detective Koch at (925) 779-6895.