This paper reports on a theme, the intrusion of the Traditional Western worldview, emerging from an ongoing study of the impact of teachers' engagement in the Transreform approach to the teaching and learning of mathematics on students' affective and cognitive responses to and achievement in mathematics. Newly theorized (Russell & Chernoff, 2011, 2012), the Transreform approach occurs when the teaching and learning of mathematics is grounded within an Indigenous worldview. This paper identifies and analyzes incidents captured within the study's data that demonstrate ways in which the Traditional Western worldview can intrude on an Indigenous worldview and upon the teaching and learning of mathematics. [The authors of this paper acknowledge partial funding of this research by the Dr. Stirling McDowell Foundation for Research Into Teaching. For the complete proceedings, see ED584443.]