The 17-year-old girl was finishing her final year of high school in Melton when Korczynski, then aged in his 30s, started inviting her into his office.

The now-49-year-old took the teen to football matches and drove her home from parties, kissing her in secluded car parks.

He sexually assaulted the girl in the back of his car a few months into their so-called relationship.

They continued to see each other after the girl turned 18 and finished school, but she ended things a few months later.

The woman came forward to police in 2017 and Korczynski was charged three years later.

He pleaded guilty in the Victorian County Court earlier this month to a charge of sexual penetration of a child under his care.

Korczynski's offending was "wholly inappropriate" and there was an enormous power imbalance in play, Judge Fiona Todd said on Friday.

He knew he was doing the wrong thing as other teachers called him out on his behaviour, the judge said in her sentencing remarks.

The woman still feels intense shame, embarrassment and isolation as a result of Korczynski's actions, Judge Todd said.

She accepted the 49-year-old had no prior convictions, he had not reoffended, and he had been stripped of his teaching licence as a result of the charges.

But Korczynski's sentence needed to send the message to the community that teachers had a duty of care to their students that could not be abused.

Korczynski was sentenced to a 19-month jail term that was wholly suspended for three years.

As long as he does not offend in that time period, he will not be imprisoned.

Korczynski will be on the sex offenders register for 15 years.

Australian Associated Press