The principles and practices of progressive education gained wide acceptance in American school systems during the first half of the 20th cent.; similar pedagogical innovations were instituted in many of the schools of Europe. From its inception, however, the movement elicited rather sharp criticism from a variety of different sources, particularly for its failure to emphasize systematic study of the academic disciplines. Opposition increased greatly in the years following World War II, and many hold that by the late 1950s the movement had collapsed. By that time, however, the progressive movement had effected a permanent transformation in the character of the American school, and many progressive schools across the country were firmly established. Other educational reform movements that have been affected by or are similar to progressive education are open education, the Summerhill school, and the reforms of Maria Montessori.