The quandary of diagnosing mathematical difficulties in a generally low performing population

Brazilian students’ mathematical achievement was repeatedly observed to fall below average levels ofmathematical attainment in international comparison studies such as PISA. In this article, we argue thatthis general low level of mathematical attainment interferes with the diagnosis of developmentaldyscalculia when the psychometric criterion is used: establishing of an arbitrary cut-off (e.g., performance< percentile 10) may lead to misleading diagnoses. Therefore, the present study set off to evaluate theperformance of Brazilian school children on basic arithmetic operations. Seven hundred and six childrenfrom 3rd to 5th grades completed a calculation task assessing arithmetic fluency in addition, subtraction,and multiplication. In line with PISA results, children presented difficulties in all arithmetic operationsinvestigated. Children performed better in addition than subtraction and multiplication, and 3rd and 4thgraders were outperformed by 5th graders in all three operations. However, even after five years offormal schooling, less than half of 5th graders performed perfectly on simple addition, subtraction, andmultiplication problems. Therefore, these data substantiate the argument that the sole use of apsychometric criterion might not be sensible to diagnose dyscalculia in the context of a generally lowperforming population, such as Brazilian primary school children. When the majority of children failthe task, it is hard to distinguish atypical from typical numerical development. As such, other diagnosticapproaches, such as Response to Intervention, might be more suitable in such a context.