This article analyzes the answers given to an item related of the standardized Maths test administered in May 2015 to all fifth grade primary students in Canton Ticino. Starting from the statistical results emerged from a sample of 508 selected protocols, a qualitative analysis on a shorter sample of 174 students of first year of secondary school has been performed, to trace the causes of the difficulties emerged in the resolution. From this analysis we found that many wrong answers are related to difficulties in understanding the item text, in particular to linguistic interpretation. Considerations made may provide teachers tools for diagnosing specific difficulties and suggesting “intervention areas”.