Andrew John Medeiros, 25, of Santa Rosa, pleaded no contest in June to oral copulation with the teen. He faced three years in prison.
A charge alleging digital penetration was dismissed as part of his plea deal.
Deputy District Attorney Rosanne Darling said Medeiros "groomed" the girl by exchanging text messages with her for approximately a year before the sexual contact occurred in March and April.
Darling said the girl was taken aback by the text messages, in which Medeiros described the sexual acts he wanted to perform with her.
In a letter to Sonoma County Superior Court Judge Jamie Thistlethwaite, the girl's family said she trusted Medeiros as her coach and didn't know how to get out of the situation.
"School was one place we thought she was safe," the family said in the letter.
Darling had asked the judge to sentence Medeiros to a year in county jail.
Defense attorney Richard Scott said Medeiros really believed he was going to have a lifelong relationship with the girl, and is now "devastated" because he realizes the magnitude of the offense and blames no one but himself.
A psychiatrist who examined Medeiros concluded that there is a low or moderate risk of him re-offending, and Thistlethwaite did not order him to register as a sex offender unless he violates his four years' probation.
Scott had argued against the sexual offender registration, calling it "a death sentence."
Medeiros also must participate in an outpatient treatment program for sex offenders when he is released from jail.
"Sitting in custody is not appropriate. You need treatment and help," Thistlethwaite said.
Medeiros also coached for the North Bay Elite Basketball Club for elite high school female players. He was arrested April 11 at Piner High School in Santa Rosa, where he was a student supervisor.