N.J. Stat. Ann. § 18A:22-1

There shall be in each type I district a board of school estimate, which shall consist of two members of the board of education appointed by it, two members of the governing body of the municipality appointed by it, and the mayor or other chief executive officer of the municipality or if there be no chief executive officer then an additional member appointed by the governing body. Appointments shall be made annually in December, and vacancies shall be filled immediately by appointment as the original appointments were made for the unexpired terms.