Romina Jamieson-ProctorThe development of place value understanding is an essential foundation concept that enables students to have a strong number sense. However, place value is a common problem area experienced by students and pre-service teachers alike. This paper reports the results of an initial investigation of pre-service teachers? understanding of the symmetry of the place value system. The results suggest that pre-service teachers’ mathematical content knowledge with respect to the symmetry of the place value system is weakest for fractions and when they are asked to generalise their understanding to a base a system. Overall more of the pre-service teachers had a pre- or uni-structural understanding of the symmetry of the place value system.