The didactic contract to interpret some statistical evidence in mathematics standardized assessment tests

In this study we analyse results of Italian standardized tests in mathematics integrating quantitative analysis based on the Rasch Model and didactical interpretation. We use specific graphs to analyse the trend of each answer as function of the students' math ability. This approach led us to focus on specific items in which a wrong answer results particularly popular among medium/high level students and analyse this particular trend with the lenses of math education theories. The study reveals that these phenomena are particularly related to implicit and explicit rules governing classroom practices exist at all school levels and regard different mathematical content and skills.