Purpose: Elementary teachers' understanding of mathematics is a significant contributor to student success with mathematics. Consequently, teacher educators are frequently charged with the responsibility of supporting the development of prospective elementary teachers' mathematics content knowledge as they re-learn concepts in ways they are required to teach. The purpose of this paper is to describe one teacher educator's efforts to support prospective elementary teachers' tenuous understanding of rational numbers. Design/methodology/approach: Given the variety of factors influencing the development of teacher knowledge, a mixed method research design was utilized. Research participants were prospective elementary teachers enrolled in a nine-week elective course who agreed to participate in the study (n=40); while the control group were prospective elementary teachers not enrolled in the elective course (n=35). Findings: The results of this study indicate that it may be possible to improve prospective teachers' conceptual understanding of mathematics by providing additional short-term support, such as an elective course and/or web-based video clips. However, the program intervention can only build upon the existing knowledge that prospective teachers bring when they begin their Bachelor of Education programs. Originality/value: For prospective teachers with a limited foundation in mathematics (e.g. less than four secondary school mathematics courses), short-term support may be insufficient to compensate for their nebulous understanding of rational numbers. Based on this finding, one-year Bachelor of Education programs might consider, either: including Grade 12 mathematics as a pre-requisite for elementary teacher applicants; or mandating enrolment in a full-year math content course similar to the elective course described in this paper. (Contains 4 tables.)