LEWISTON — An Androscoggin County grand jury on Tuesday indicted a former teacher at Pine Tree Academy in Freeport on 26 charges related to his alleged sexual assault of a 15-year-old female student at the Seventh-day Adventist school on Pownal Road.

Derek Michael Boyce, 37, of Woolwich admitted to police that he had sexual contact with the student after her mother caught them at her Lisbon home in September, according to an affidavit filed in Androscoggin County Superior Court.

Boyce is charged with 12 counts of gross sexual assault and eight counts of sexual abuse of a minor, each count punishable by five years in prison. Boyce, the girl’s math teacher at the Christian school, also was charged with six counts of unlawful sexual contact, punishable by up to 364 days in jail.

Boyce remained Tuesday at the Androscoggin County Jail in Auburn, where he was being held on $50,000 bail.

In September, he was placed on leave by Pine Tree Academy, which has 126 students in grades K-12, and was later terminated.

The girl told her mother she had had sexual intercourse with Boyce before.

Boyce told police that he and the girl began communicating via social media messaging applications after she suffered a sports injury and had been depressed. He told police that they became romantic and had sex in July. Boyce told police that the sexual contact was consensual and that no drugs or alcohol were involved.

He has no criminal history in Maine, according to the State Bureau of Identification.

Pine Tree Academy is owned and operated by the Northern New England Conference of Seventh-day Adventists and has been open since 1974. Its curriculum offers Christ-centered learning for kindergarten-through-12th-grade day students and a limited number of boarding students from New Hampshire, Vermont and Maine.

As a private school, Pine Tree Academy is not required to hire certified teachers and Boyce is not state-certified.

He passed a standard pre-employment background check that included multiple reference interviews, a spokesman for the Northern New England Conference of Seventh-day Adventists said.

“Rigorous background checks are conducted on all teachers during the hiring phase,” Scott Christiansen said in September. “Background checks include all law enforcement records, including traffic violations, as well as multiple interviews with references and previous employers. As a teacher at Pine Tree Academy, such a background check was done on Mr. Boyce.”

Correction: This story was updated at 12:30 p.m. Wednesday, Dec. 5, 2018.  Because of an editing error, the story misstated his employment status. He has been fired, according to a school spokesman.

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