Any driver who has accumulated points under the provisions of this article shall have the number of his points reduced by four upon proving to the satisfaction of the department that he has completed the National Safety Council's "Defensive Driving Course" or its equivalent, if the course is completed after the points have been assessed. The course must be taught by an instructor accredited by the National Safety Council whose procedures for accreditation are set forth in "Manual of Rules and Procedures" published by the National Safety Council or equivalent accreditation procedures. The department shall establish procedures by which driver training schools may apply to the department for approval of a defensive driving course which will qualify those successfully completing the course for a reduction in points pursuant to this section. The department shall approve the National Safety Council's "Defensive Driving Course" or its equivalent when offered by driver training schools and taught by an instructor accredited by the National Safety Council or equivalent accreditation procedures. No person's points may be reduced more than one time in any three-year period by the method provided for in this section.