Tajreed Rich, a hall monitor at Robbinsdale Cooper High School in Minneapolis, was allegedly caught in bed with an unidentified 17-year-old female student by the girl's father.
Rich, 41, was charged with sexual assault last Friday.
The father reportedly heard some strange noises when he came home at about 3 p.m.
He walked into his daughter's bedroom and saw Rich, naked, standing near his daughter, who was naked on the bed, reported CBS Minnesota.
The dad recognized Rich and called police later that day.
Rich, who counseled students about relationships and coached a cheerleading team, was fired by Robbinsdale Cooper High School on Monday.
The 17-year-old girl claims that she had sex with Rich twice, which he confirmed to police, according to the Star Tribune.
Rich reportedly described the girl as a "vulnerable student" and knew he should not have had sex with her, which he did without a condom.
"This is a horrible incident, and the district finds acts such as this reprehensible," said Robbinsdale Cooper High School in a statement. "The safety and well-being of our students is our top priority, and our hearts go out to the family during this time."
Rich is being held in Hennepin County Jail. He faces up to 15 years in prison and a $30,000 fine if convicted.