The study described here is a longitudinal qualitative case study conducted on a mathematics pre-service teaching program at a university in Southeast Asia. The university program of study required all pre-service teachers of mathematics to be involved in an alternative form of field experience in which the pre-service teachers would enact mathematics camps for college freshmen and for K-12 students. The pre-service teachers were expected to take on increased responsibility for the success or failures of the mathematics camps as they matriculated through the program. Constant comparative analysis revealed a "peer mentoring professionalism" among the pre-service teachers as they negotiated the challenges of teaching mathematics during these alternative field experiences. Description of the construct of "peer mentoring professionalism" as well as explanation of its derivation from the study are given. Implications and applicability across mathematics teacher education programs are discussed.