Gov. Jerry Brown rejected legislation on Thursday requiring that California middle and high schools start no earlier than 8:30 a.m.
Supporters of the bill cited research that says delaying school start times could result in better grades, attendance and graduation rates.
A study by the American Academy of Pediatrics said insufficient sleep for teens was "an important public health issue that significantly affects the health and safety" of adolescents.
State Sen. Anthony Portantino, who carried SB 328, cited that study and one by the Centers for Disease Control and Prevention that both suggested schools start at 8:30 a.m. or later to help students get the optimal amount of sleep of at least eight hours a night.
Middle and high schools in California start their school day on average at 8:07 a.m., according to the CDC study.