CHULA VISTA, Calif. -- A junior high history teacher from National City pleaded guilty Monday to carrying on a sexual relationship with a 15-year-old female student.

During a hearing at the South Bay Courthouse, 37-year-old Craig Edward Kelso entered into a plea agreement that calls for him to be sentenced on Oct. 7 to four years and four months in state prison.

Kelso -- a teacher at Granger Junior High -- pleaded guilty to having sex with a minor, committing a lewd act on a child 14 or 15 years old and oral copulation on a person under 16.

Eighteen other charges, including trying to dissuade a witness from reporting a crime, were dismissed as a result of Kelso's guilty plea.

Deputy District Attorney Enrique Camarena said earlier that the relationship between Kelso and the teenager began last December and turned sexual in March. The two had sexual encounters in several places in San Diego, including on the Granger campus, the prosecutor said.

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 July 15.

A report that Kelso might be at the high school turned out to be erroneous, and he was arrested in downtown San Diego later that night.

Kelso went missing shortly after the molestation allegations came to light and was a fugitive for several days, authorities said.