A Queensland Catholic school did not tell parents or police about sexual abuse allegations against a teacher for more than a year, an inquiry has heard.

Complaints of abuse were first made against Gerard Byrnes in 2007 but he remained working as a teacher at the school until he resigned in June 2008, the royal commission into institutional responses to child sexual abuse in Brisbane was told on Monday.

A month later, Byrnes was re-employed as a relief teacher at the school in July and held the position until he was arrested that November. Over his course of employment at the school he sexually abused 13 girls.

The principal, Terence Hayes, the school’s student protection officer, Catherine Long, and the Catholic Education Office were aware of the sexual abuse complaints and took no action, the commission was told.

Hayes was said to have told one girl’s father he would deal with her abuse complaint internally in September 2007 but denied knowing anything when police informed other parents their daughters had also been abused in 2008.

A mother, known as KP, told the inquiry that after police swooped on the teacher, the Catholic Education Office and the school denied any prior knowledge of the abuse.

“I found out later, through media reports and court processes, that this was not even true. Mr Hayes was aware of complaints about Mr Byrnes for over a year but did not report them to police,” KP told the inquiry by videolink.

“A report should have been made to the police straight after the first complaint was made to the school. If this had happened, KC and the other girls would not have been abused.”

Another mother, known as KO, was told by police that her daughter, KA, had been abused by the teacher in 2008.

At KA’s birthday party another girl told KA that she and her father had met Hayes and told him she had been abused by the teacher in 2007.

“Terry Hayes had told the family at the time the school would deal with it,” KO told the inquiry via videolink. “The family then moved to Brisbane not long after, so nobody else knew what Mr Byrnes was doing to the girls. We weren’t warned or informed by the school.”

Long told the commission she could not believe that 13 girls did not have the courage to speak out about being sexually abused by their teacher.

Long, who is still a teacher at the school, was present at a 2007 meeting between Hayes and a girl who had a complaint about being abused by Byrnes.

She said although she was the school’s student protection officer at the time, she did not report the complaint to police. “No, I didn’t think I was in charge of the situation,” Long said.

“I was there as the note taker. The principal was there. He was in charge, not me, and that’s not passing the buck, that’s where I thought we stood.”

Byrnes was eventually arrested in 2008 before being jailed for 44 counts of child sex abuse in 2010.

Long said Byrnes had regularly given lollies to schoolgirls and they were seen “hanging off him” when he was on playground duty, but she hadn’t seen his actions as grooming.

But Long also said she still struggled to believe that her colleague could have abused so many girls with so many other adults around without anybody noticing.

“I don’t get that our children, with all of the student protection and everything else we have, didn’t have the courage to come forward,” she told the inquiry.

“They didn’t speak to us, the people they knew and trusted supposedly, they couldn’t talk to their parents, and you heard their mums today, they still haven’t spoken up.

“Why? What is it that’s caused this, that’s stopped these kids from speaking out? So I struggle with it.”

The inquiry was adjourned until Tuesday morning.