The purpose of the study was to understand how a program based on educative supervision supported the supervisory knowledge and practices of mathematics cooperating teachers. Educative supervision referred to a supervision style where the supervisors challenge student teachers' teaching methods by asking open-ended questions, discussing critical incidents from their teaching, moving away from being evaluative, and being sensitive to their zone of proximal development (Blanton, Berenson, & Norwood, 2001). The case study method was followed in this study, where the case was the designed program. The program consisted of online discussions on reading materials or video clips, face to face communications, conducting weekly post-lesson conferences with the student teachers, and reflections on those post-lesson conferences. Three mathematics cooperating teachers and their student teachers were the participants of this study. Qualitative data analysis techniques were applied to all data sets to understand how the program supported the supervisory knowledge and practices of the cooperating teachers. Data was mainly analyzed from three perspectives. First, the amount of conversational time used by each participant was calculated. Secondly, content of the post-lesson conferences was classified into the following categories: Mathematics, Pedagogy, Mathematics Pedagogy, Teacher-Student Relationship, Classroom Management, and General Teacher Growth. Thirdly, the types of communications used by each participant were collapsed into the following categories: Questioning, Assessing, Suggesting, Describing, Explaining, and Emotional talking. Data analysis indicated some changes in the supervision style of the participating cooperating teachers towards the educative supervision. First, the percent of talking done by the student teachers in the post lesson conferences increased after the discussion of educative supervision in the program. Secondly, mathematics pedagogy became the most discussed content category in the post-lesson conferences. Furthermore, the depth of talks on mathematics pedagogy grew. Thirdly, the cooperating teachers moved away from conveying their feedback directly to the student teachers; they started asking open-ended questions to have the student teachers reflect on their teaching. Finally, having student teachers reflect on their teaching became a central goal for all of the cooperating teachers.