The department of education shall consist of the county school board, the division superintendent of schools and the officers and employees thereof. Except as herein otherwise provided, the county school board and the division superintendent of schools shall exercise the powers conferred and perform the duties imposed upon them by general law. The county school board shall be composed of not less than three nor more than seven members, who shall be chosen by the board of county supervisors. The exact number of members shall be determined by the board. Notwithstanding the foregoing provisions of this section, the county school board in a county which is contiguous to a county having the urban county executive form of government shall consist of the same number of members as there are supervisors’ election districts for the county, one member to be appointed from each of the districts by the board of county supervisors. The board may also appoint a county resident to cast the deciding vote in case of a tie vote of the school board as provided in § 22.1-75. Any tie breaker shall be appointed for a four-year term whether appointed to fill a vacancy caused by expiration of a term or otherwise. The chairman of the county school board, for the purpose of appearing before the board of county supervisors, shall be considered head of this department, unless the school board designates some other person in the department for such purpose.