A Sydney school teacher has broken down in court as a jury found her not guilty of having a sexual relationship with a male student.

The 30-year-old woman, who cannot be named for legal reasons, wept uncontrollably as the verdict was handed down in Downing Centre Local Court on Tuesday afternoon.

A large group of family and friends also cried in the courtroom and one supporter walked out of the court and cheered.

The woman said "thank you" to the jury as they were being dismissed.

The woman had pleaded not guilty to three counts of having sexual intercourse with the teenager who was under her care.