105 ILCS 5/9-5

The dates upon which school officer elections shall be held are as established in the general election law. Members of boards of education shall unless otherwise provided serve terms of 4 years. If, at a regularly scheduled election, a proposition is submitted to the voters of a district, as provided by a resolution of the board, on the question of whether board members should serve for 6 year terms and the proposition receives the affirmative vote of those voting thereon, members of the board of education shall thereafter serve for terms of 6 years.