The purpose of this paper is to describe a typology of instructor discourse interventions to enhance mathematical discourse in online asynchronous discussions in a statistics course for teachers. A completely asynchronous model of distance delivery was used for the course. Emphasis was given to fostering mathematical discourse in that the students were encouraged to state their ideas, elaborate on their thinking, and compare their ideas with previously shared ideas. Using the constant comparative methodology for developing theory, the analysis of asynchronous discussions revealed 5 recurring categories of response with respect to instructor intervention: (a) resolve, (b) validate, (c) redirect, (d) expand, and (e) withhold. With respect to the identified typology, the authors recommend that the default action on the part of the instructor be to withhold, using one of the other interventions only if necessary. Withholding encourages the students to lead and become active participants in the discussion, thus enhancing mathematical discourse. The paper also discusses implications of the findings and recommendations for future research.