Santa Margarita High quarterback K.J. Costello announced his commitment to Stanford over Michigan and USC on Thursday.
"It was definitely a hard decision I made passing [USC] up," said Costello, whose mother attended USC.
Costello, 6 feet 5 and 220 pounds, said playing for the Trojans was a childhood dream, but he decided on Stanford after learning more about its academics and team.
"I kind of see what the future holds as far as after football and everything that comes along with a Stanford degree," he said.
Costello is the third quarterback in the 2016 class to turn down the Trojans.
Former Westlake High quarterback Malik Henry, who transferred to IMG Academy, committed to
USC has not offered scholarships to any other quarterbacks.
It is possible USC might not take a quarterback in the 2016 class after signing Ricky Town and Sam Darnold in 2015.