Education in Mexico has a long history. Indigenous peoples created institutions such as the telpochcalli and the calmecac. The Royal and Pontifical University of Mexico, the second oldest university in the Americas, was founded by royal decree in 1551. Education in Mexico was, until the early twentieth century, largely confined to males from urban and wealthy segments and under the auspices of the Catholic Church. The Mexican state has been directly involved in education since the nineteenth century, promoting secular education. Control of education was a source of an ongoing conflict between the Mexican state and the Catholic Church, which since the colonial era had exclusive charge of education. The mid-nineteenth-century Liberal Reform separated church and state, which had a direct impact on education. President Benito Juárez sought the expansion of public schools. During the long tenure of President Porfirio Díaz, the expansion of education became a priority under a cabinet-level post held by Justo Sierra; Sierra also served President Francisco I. Madero in the early years of the Mexican Revolution. The 1917 Constitution strengthened the Mexican state's power in education. During the presidency of Álvaro Obregón in the early 1920s, his Minister of Public Education José Vasconcelos implemented a massive expansion of access to public, secular education and expanded access to secular schooling in rural areas. This work was built on and expanded in the administration of Plutarco Elías Calles by Moisés Sáenz. In the 1930s, the Mexican government under Lázaro Cárdenas mandated socialist education in Mexico and there was considerable push back from the Catholic Church. Socialist education was repealed during the 1940s, with the administration of Manuel Ávila Camacho. A number of private universities have opened since the mid-twentieth century. The Mexican Teachers' Union (SNTE), founded in the late 1940s, has had significant political power. The Mexican federal government has undertaken measures to reform education, which have been opposed by the SNTE. Education in Mexico is currently regulated by the Secretariat of Public Education () (SEP). Education standards are set by this Ministry at all levels except in "autonomous" universities chartered by the government (e.g., Universidad Nacional Autónoma de México). Accreditation of private schools is accomplished by mandatory approval and registration with this institution. Religious instruction is prohibited in public schools; however, religious associations are free to maintain private schools, which receive no public funds. In the same fashion as other education systems, education has identifiable stages: