Gwinnett County police are investigating another allegation that a Gwinnett public school teacher had an inappropriate relationship with a student. It’s the school system’s fourth such case this year.

The teacher is accused of engaging in sexual activity with a 17-year-old South Gwinnett High School student on several occasions since March, police said. The unidentified teacher resigned Tuesday, said Gwinnett school district spokeswoman Sloan Roach. She had been teaching at South Gwinnett High School since 2002.

Roach said the student’s parent contacted school officials with the allegations. School district human resource officials began an investigation. The case was forwarded to county police, and the state Division of Family and Children Services was also notified. Gwinnett police were asked to investigate because some of the alleged activity took place at the teacher’s home and at Lenora Park, near Snellville.

Under Georgia law, sexual contact between anyone with supervisory or disciplinary authority — such as a law enforcement officer, teacher or psychiatrist — and a person under their care is illegal, even if it is consensual.

Gwinnett police spokeswoman Michele Pihera said investigators haven’t interviewed the accused former teacher yet.

Three other educators who taught in the Gwinnett system at the start of this school year have been charged with sexual misconduct with students.

Here’s a breakdown of the other Gwinnett cases:

Michael Appelbaum was arrested Tuesday on child molestation charges against two former Gwinnett School of Mathematics, Science and Technology students.

James Buckland, an instructor at Summerour Middle School, was charged in early October with sexual battery of a student.

Julee Impara voluntarily surrendered her Georgia teaching certificate last month after being arrested on charges she had a sexual relationship with a student she taught at Mill Creek High School.