By mid-century many public school programs had also adopted elements of progressive curriculum. At mid-century Dewey believed that progressive education had "not really penetrated and permeated the foundations of the educational institution."(Kohn, Schools, 6,7) As the influence of progressive pedagogy grew broader and more diffuse, practitioners began to vary their application of progressive principles. As varying interpretations and practices made evaluation of progressive reforms more difficult to assess, critics began to propose alternative approaches.