The school committee shall appoint a superintendent of schools as its chief administrative agent who shall have under the direction of the school committee the care and supervision of the public schools and shall have and exercise such duties and authority as are vested in the office by the laws of the state, the state board of education and the commissioner of education. No person shall be employed as the superintendent of schools unless such person holds a certificate of qualification for said office issued by or under the authority of the state board of education.