Laura Elizabeth Whitehurst, 28, was arrested by Redlands Police at about 8:45 p.m. Monday at her Redlands residence after being questioned.
Whitehurst was a teacher at Citrus Valley High School. She was placed on administrative leave by the Redlands Unified School District Tuesday following Monday's arrest. The district then secured her resignation.
Whitehurst was an adviser to the then-16-year-old boy, who is now 17.
The victim's mother reported the relationship to school officials, who contacted Redlands Police Monday. The sexual relationship allegedly began in the summer of 2012 and continued for nearly a year, police said.
Whitehurst gave birth to a child on June 18; the teen is the father, according to police.
Whitehurst was arrested for unlawful sexual intercourse with a minor. She posted $25,000 bail and was released Monday evening, police said.
The investigation was continuing.
Anyone with additional information related to the case is asked to contact Detective Natasha Crawford at (909) 798-7623 or Redlands Police Dispatch at (909) 798-7681.