Tallman (2015) argued that pedagogical content knowledge is a form of content knowledge with particular characteristics that endow it with pedagogical utility, and he conjectured that an essential characteristic of a teacher's content knowledge is her conscious awareness of the mental actions and conceptual operations that comprise her mathematical schemes. We report the results of a study that explored this conjecture by examining the pedagogical implications of engaging a pre-service secondary teacher in a mathematical intervention to support her construction of a powerful scheme for constant rate of change and to engender her conscious awareness of the mental processes that constitute this scheme. [For the complete proceedings, see ED606531.]