Monica Young had been due to face trial in September on 12 charges, but today reached a plea deal, the same day her teenage victim was due to pre-record his evidence.
The 24-year-old pleaded guilty to three counts of aggravated sexual intercourse with a child.
The high school teacher was arrested at her Greenacre home in July last year.
Prosecutor Alexander Terracini told the court he would be arguing prison time was the only option for Ms Young.
She’ll face a sentencing hearing on June 24.