Complex sentence: Most schooling was done in the one room school houses by teaching students of various ages and abilities together using the Monitorial System, an education method that became popular on a global scale during the early 19th century.
Split into simpler sentences: Most schooling was done in the one room school houses. By teaching students of various ages and abilities together using the Monitorial System, an education method that became popular on a global scale during the early 19th century.