§ 3005-a. Leave of absence for teaching purposes. In a city of one million or more, a board of education may permit any teacher to apply for and receive a leave of absence for a period not to exceed two years for teaching in a college or university, certificated and accredited by the commissioner of education, provided such college or university shall have agreed to furnish an educator of professorial rank to fulfill the duties of the said teacher on leave of absence or any other duties assigned by the superintendent of schools. During the period of said leave of absence for teaching in a college or university, the said teacher shall receive from the school district in said city the same compensation that he would have received had he been present and teaching in a school of the district and the college educator if he is a member of a publicly operated college or system shall likewise receive the same compensation as he would have received had he remained in the college or university. Such leave of absence shall not in any way affect the retirement rights of the said teacher or college educator as a member of a retirement system and the period of the aforesaid leave of absence shall be credited to the total years of service of the said member in the same manner and for all purposes as if he had continued in his position. Notwithstanding any of the provisions of this chapter, nor any other local law or provision, the chancellor of the city board shall have authority to issue to such college or university educator a special certificate of competency which shall be valid for a period not to exceed two years and not renewable and under which such college or university educator shall be permitted to fulfill the duties and assignments as herein provided.