A legal loophole has allowed a teacher back in the classroom despite having taught unlawfully and having sex with a 16-year-old student.

Four years ago, the Herald on Sunday revealed Natasha Miller, then 23 and teaching at Tararua College in the Wairarapa, was having an affair with student Hayden Macdonald.

She resigned, and the two gave an intimate, tell-all interview to a women's magazine headlined: "I fell for my student".

Now, this paper has learned that:

She was never legally registered to teach in the first place, according to the Teachers Council.

Because she was not a registered teacher, no conduct complaint was ever laid with the Teachers Council.

She is back teaching at Dannevirke High School, just up the road - this time with provisional teaching registration.

She and Macdonald are engaged and have a 4-month-old baby named Harlow.

Approached at their home in Pahiatua, Macdonald told the Herald on Sunday that he wanted to be a teacher, too. Dannevirke High School has given him work as a part-time music tutor, and he appears in the staff photo with Miller.

He said it was "pretty cool" to be a dad, and that Harlow was "a good baby".

He was studying at university to become a full-time music teacher, he said, following his passion for playing the guitar.

In 2006, Miller told this paper that she did not expect to ever be allowed to teach again, after the affair and her resulting resignation.

That has not been the case. She now works at Dannevirke High, only 30 minutes' drive from Tararua College. The school employed her as an automotive instructor barely a year after her resignation from Tararua College and she now works as an English teacher.

Miller, a former New Zealand women's football representative, was also given the responsibility of coaching the 1st XI schoolboy football team.

Dannevirke High School principal Mike Tribe said he rang the Teachers Council before hiring Miller and was told she had never been investigated.

Tribe had known about Miller's affair because it happened locally. When he employed her, he received complaints from parents, teachers and others in the Dannevirke community.

"There were eyebrows raised as it was a famous case around here," he said.

But he believed she was an "excellent" teacher and deserved a second chance in the profession.

However, sources in the Dannevirke school community disagreed. One believed she should never have been allowed to teach again, and that a male teacher would have been "lynched".

Tararua College principal Glynis De Castro, who employed Miller, refused to comment. Tararua board chairwoman Ann Beech also declined to comment.

But the acting principal of Tararua College at the time, Alan West (now retired), said it was De Castro who had signed Miller's employment papers.

Teachers Council director Peter Lind said Miller had been "operating unlawfully" as a teacher at Tararua College.

She had been training to be a teacher, but had not yet gained registration. This meant the council had "no authority" to investigate her.

"We couldn't deal with that situation," he said. "It was a very unusual situation."

Because she now has provisional registration, Miller was entitled to work as a teacher and there was nothing the Teachers Council could do about it.

Generally, if a teacher had an affair with a pupil, it was a "very serious" breach of the code of ethics and should be referred to the council for investigation.

The council had not dealt with any complaint against Tararua College for employing an unregistered teacher, Lind added, but the council now monitored the school to make sure its hiring practices complied with the law.

Labour's education spokesman Trevor Mallard said Miller appeared to have escaped "on a technicality" that some might view as unfair.

He said the teacher-pupil relationship was "not ethical" and he hoped the Teachers Council's increased powers would stop such a breach ever being repeated.

Education Minister Anne Tolley would not comment on the individual case but said she was talking to the Teachers Council about improved transparency.

It was vital that students were safe at school, she said, and that parents had peace of mind.

To that end, the Government had introduced new laws to improve student safety by enabling the Teachers Council and the Ministry of Education to share information to identify unregistered teachers.