GOLDEN, Colo. -- The trial for a former Dakota Ridge High School teacher and tennis coach accused of sexually assaulting a student continued Wednesday, where his defense argued that he thought the girl he was in a relationship with was 18 years old.

Kevin Ponis, 36, was arrested in May, accused of grooming teenaged girls on the tennis team for sex. He faces charges of sexual assault on a child by a person in a position of trust, and a pattern of sexual assault on a child by a person in a position of trust.

His accuser testified Wednesday said she was 17-year-old senior at Dakota Ridge when she began a consensual sexual relationship with her tennis coach. She said she had developed a crush on him, and looked up to him and during one point, he had told her, "Think of me as a big brother. I will always be there for you."

Because the relationship appears consensual, the girl's age during the 2000 and 2001 sexual encounters is crucial.

The defense said Ponis' accuser told others she was 18 years old, giving Ponis the impression that she was of legal age. His defense attorney, Craig Truman, argued in his opening statement Tuesday that the girl, who was in therapy for anorexia, told her therapist that she was 18 and had sex with her teacher. Truman said that when it was convenient for her, she said she was 17, and when it was inconvenient for her, she was 18.

Truman argued that the woman, who is now 21, only came forward when she learned that he had a sexual relationship with another former member of the tennis team.

Two other women are scheduled to testify that Ponis engaged in sex with them but only after they turned 18.

However, prosecutors said Ponis could have easily checked school records and athletic rosters to learn the teen's true age. They claimed he got to know the girls when they were younger, started giving them compliments and extra attention and then had sexually suggestive conversations with them. Prosecutor Steve Jensen said Ponis then "picked up the level of sexual advances" when they were of legal age.

The prosecution claims Ponis violated his position of trust as a teacher, coach and student government sponsor to prey on his students.

"This is a case about a breach of trust, a gross violation of the position of trust," Jensen said.

Jensen, in his opening statement, said he has audio tape with Ponis admitting that he had sexual relations with one of the girls when she was 17. A lot of the sexual activity happened three or four times a week after hours at the school -- in locked classrooms and secluded locations where Ponis used his master keys to gain access -- and Ponis even videotaped the encounters, Jensen said. Officials had said they found at least one of the videos on his personal computer when they confiscated it. Jensen said Ponis had used video equipment at the school to videotape some of the encounters, but the tapes have been destroyed.

Truman told the jury that Ponis' actions may be regrettable, or worse, but they are not a crime.

"While his conduct may have been reprehensible, there's a reason for it," Truman said. "There was a hole in his heart he tried to plug up with the adoration of these young girls. He was willing to risk everything for relationships with these young women."