This paper describes Singapore and Australian Grade 6 students' (n=1,187) performance on a symmetry task in a recently developed Mathematics Processing Instrument (MPI). The MPI comprised tasks sourced from Australia and Singapore's national assessments, NAPLAN and PSLE. Only half of the cohort solved the item successfully. It is possible that persistence of prototypical images of a vertical line of symmetry and reinforcements in the classrooms could have attributed to this low success rate.