A former high school teacher who had sex with underage girls had largely kept the relationships secret but had included his partner in some of the acts, a Perth court has been told.

Brett Rodney Daley, 34, has been sentenced to seven-and-a-half years in jail for having sex with a child aged between 13 and 16, and sex with a girl aged 16 years who was in his care.

The offences occurred over several months in 2006.

At the time, Daley, a former high school teacher and a community soccer coach, was in a relationship with a 19-year-old woman who is also accused of having sex with the youngest of the two students.

The woman, Natasha Charmaine Krispyn, now has a one year-old child to Daley, the District Court in Perth was told on Thursday.

Daley’s lawyer, Laurie Levy, argued that his client’s acts had involved women almost at the age of consent, and that there was no violence, intimidation or coercion involved.

But Judge Mary Ann Yeats told Levy that Daley appeared to have an “inappropriate interest” in young girls.

She said Daley, who was aged 32 at the time, had often gone behind his partner’s back in having two ongoing sexual relationships with the complainants.

While Krispyn later took part in some of the acts, Daley had carried out many of his sexual relationships in secret.

“He was in a relationship at the time with a woman of … 19,” Judge Yeats told the court.

“It appears (the man) has an … inappropriate interest in young women.”

Judge Yates said Daley had caused life-long trauma and stress to his victims.

She said that although the sexual acts were consensual, the girls, one aged 15 and the other 16, did not have the emotional maturity to handle their experiences.

Krispyn received a suspended sentence for taking part in one of the sexual acts.
 
“When we have a one-year-old child we look very carefully at whether both parents need to be in prison,” the judge said.

Daley will be eligible for parole in five-and-a-half years.