Robert M. Swalstad, 31, also was ordered by Stevens County Superior Court Judge Allen C. Nielson not to have contact with any girls under the age of 18, with the exception of his now-16-year-old wife.
Swalstad pleaded guilty to a single gross misdemeanor charge of communication with a minor for immoral purposes. Swalstad, who must register as a sex offender, could be out of jail in four months with good behavior, Nielson said.
Swalstad was accused of having sex with his wife when she was a 15-year-old freshman at Columbia High School in Hunters. He was arrested in June when the teen came forward and said she was pregnant with Swalstad's child.
The couple now lives in Wyoming, where his wife gave birth to a son Jan. 6.
Stevens County Prosecutor Jerry Wetle told the court that the case was difficult to pursue because the victim and her family initially refused to cooperate with investigators.
Swalstad originally was arrested on third-degree child rape charges. His plea agreement to the lesser gross misdemeanor charge prompted a petition campaign in the small riverside community calling for harsher punishment.
The couple moved to Worland, where Swalstad's parents live. Swalstad resigned his teaching post and Washington state education officials revoked his teaching certificate.