The services described in Sections 1750, 1751, and 1752 shall be performed by persons who hold a valid health and development credential, or life diploma based thereon, or a services credential with a specialization in health issued by the state board or Commission for Teacher Preparation and Licensing; provided, however, that a psychologist may be employed to perform psychological services or may perform psychological services under contract if he or she is the holder of a valid school psychologist credential issued by the state board.