CHULA VISTA, Calif. -- A National City junior high teacher accused of having a sexual relationship with a 15-year-old female student pleaded not guilty Friday to 21 felony counts, including trying to dissuade a witness from reporting a crime.

Craig Edward Kelso, 37, who taught history at Granger Junior High, faces more than 15 years in prison if convicted, said Deputy District Attorney Enrique Camarena.

Besides the witness-related count, Kelso was charged with 10 counts of having unlawful intercourse with a minor, two counts of committing a lewd act on a child, four counts of oral copulation on a minor, three counts of penetration by a foreign object and one count of sodomy.

South Bay Judge H. Ronald Domnitz ordered Kelso held on $900,000 bail and ordered the defendant to stay away from the victim should he make bond.

Domnitz scheduled a readiness conference for Sept. 8 and a preliminary hearing for Sept. 29.

A threat to Kelso's estranged wife, who is a teacher at Otay Ranch High School, prompted a one-hour lockdown at that school in Chula Vista on Tuesday.

A report that Kelso might be at the high school turned out to be false and Kelso was arrested that same night in downtown San Diego, authorities said.

Kelso was a wanted person for several days because he went missing shortly after the molestation allegations came to light, police Lt. Craig Boegler said.