Josefat Estrada Jr., 35, is being held in the Sonoma County jail under $235,000 bail. A preliminary hearing date was set for Feb. 17.
The alleged incidents, said to have occurred between 2005 and 2007, were reported to Sonoma police on June 25, Sonoma County Sheriff's Department Sgt. Glenn Lawrence said. Estrada was arrested at his Napa home on Nov. 16.
None of the incidents occurred while Estrada was teaching at the school. The alleged victim was 14 when the alleged sexual conduct began and Estrada was a trusted friend of the victim's family, Lawrence said.
Estrada is charged with eight counts of oral copulation of a minor, oral copulation of a minor unconscious of the act and one count of committing a lewd act on a child.
Deputy District Attorney Tashawn Sanders said the complaint alleges there is only one victim.
Sharyn Lindsey, assistant superintendent of human resources of the Napa Unified School District, said Estrada taught math at Vintage High School since the fall of 2005 and previously taught math and health at a secondary school in New York City between September 2003 and June 2004. She said he is on unpaid leave as of yesterday.
"He was very highly thought of and received good evaluations. He was a hard worker and there are nothing but good things to say about him," Lindsey said.