Probably the State Constitution.
Right you both are. New York State:
ARTICLE XI
Education
[Common schools]
Section 1. The legislature shall provide for the maintenance and support of a system of free common schools, wherein all the children of this state may be educated. (Formerly §1 of Art. 9. Renumbered by Constitutional Convention of 1938 and approved by vote of the people November 8, 1938.)