In this article, the author examines classroom observation reports from the careers of 5 teachers who taught in 14 different schools in a range of grade levels, subject areas, and neighborhoods throughout New York City. These observation reports provide an important primary source for understanding the teaching principles that guided the practices of these teachers more than 30 years. The analysis illuminates many aspects of progressivism, a movement with which many teachers and midlevel administrators would have identified during this historical period.