Developed from Noddings's (2002) care theory, von Glasersfeld's (1995) constructivism, and Ryan and Frederick's (1997) notion of subjective vitality, a mathematical caring relation (MCR) is a quality of interaction between a student and a mathematics teacher that conjoins affective and cognitive realms in the process of aiming for mathematical learning. In this paper I examine the challenge of establishing an MCR with one mathematically talented 11-year-old student, Deborah, during an 8-month constructivist teaching experiment with two pairs of 11-year-old students, in which I (the author) was the teacher. Two characteristics of Deborah contributed to this challenge: her strong mathematical reasoning and her self-concept as a top mathematical knower. Two of my characteristics also contributed to the challenge: my request that Deborah engage in activity that was foreign to her, such as developing imagery for quantitative situations, and my assumption that Deborah's strong reasoning would allow her to operate in the situations I posed to her. The lack of trust she felt at times toward me and the lack of openness I felt at times toward her impeded our establishment of an MCR. Findings include a way to understand this dynamic and dissolve it to make way for more productive interaction. (Contains 6 figures and 1 footnote.)