In October 1811, Presbyterian missionary Robert May opened an evening Sunday school in Philadelphia in which, unlike previous free schools, he taught religious doctrine solely and without remuneration. Schools resembling May's became increasingly common during the decade 1810-1820 as young, newly converted Protestants turned Sunday teaching as a means of expressing their newfound convictions. By 1820, there were several hundred Sunday school in the United States. All emphasized religious instruction over reading and writing, although most taught the later subjects as a means of inculcating the former. Many Sunday school organizers, in fact, began lobbying for extension of a system of free daily schools so that they would be free to teach religion alone on Sundays. [Robert May Sunday School Minutebook, 1811-1812, Presbyterian Historical Society.]