He credits his first rebellious influence to his sister, who had resisted their father's religious orthodoxy. Around this time, Siqueiros was also exposed to new political ideas, mainly along the lines of anarcho-syndicalism. One such political theorist was Dr. Atl, who published a manifesto in 1906 calling for Mexican artists to develop a national art and look to ancient indigenous cultures for inspiration. In 1911, at the age of fifteen, Siqueiros was involved in a student strike at the Academy of San Carlos of the National Academy of Fine Arts that protested the school's teaching methodology and urged the impeachment of the school's director. Their protests eventually led to the establishment of an "open-air academy" in .