Documenting that some features of both schooling and classroom practices slowly changed—as Parts 1,2,and 3 have done—is easy to do once buried teacher surveys, practitioner journals, and actual observations of both schools and lessons are recovered and examined across decades.

Changes in every school? Every teacher? At the same time? Of course not. While the overall pattern is stability, there is evidence for intermittent, evolving shifts in schooling and classroom practice over the years. Establishing vocational education, for example, to connect the workplace to classrooms, creating special education for children with disabilities, adding kindergartens to the age-graded school, and starting Advanced Placement courses altered the geography of schooling over the past century.

Evidence of evolving changes in teaching practice is also available (e.g., from wholly large group instruction to periodic small group activities during lessons, rearranging classroom furniture, use of new technologies). I have documented these changes…