Slidell High School Principal William Percy told parents in a letter sent home Thursday that a teacher has been arrested and is no longer an employee of the school system.

The letter said that administrators had learned of allegations of improper behavior and immediately contacted the Slidell Police Department. The school system is cooperating with police as the investigation continues, Percy said in the letter.

Slidell Police Chief Randy Smith has called an 11 a.m. news conference Friday to announce the arrest of a former Slidell High School teacher.

The notice to media said no details will be provided until the news conference.

“We are dedicated to our efforts to maintain a safe and secure and productive learning environment at Slidell High School,’’ Percy wrote. He said parents should contact him questions or concerns.

Follow Sara Pagones on Twitter at @spagonesadvocat.