Primary education students are exposed to universal assessment tests in Mathematics. The outcomes of these tests provide information which can be used to improve the efficacy of the educational system. The differentiated processed information is sent as a feedback to policy makers, school principals, teachers, students and parents. The present study aims at analyzing the performance evolution of about 100,000 Portuguese students from grade 4 to 6 in what respects competences (concepts and procedures, problem solving, reasoning and communication) and contents (numbers and operations, geometry, statistics and algebra), tested by those assessment instruments. The identification of possible problems relating either to specific competences or to particular thematic domains can help to improve successful classroom strategies. A comparative analysis of the students’ performances in 2007 (Grade 4) and 2009 (Grade 6) tests will be performed, linking these data sets with IRT models. The intent of this paper is to explain the evolution of elementary school students’ performances in Mathematics aiming at the identification of possible problems and the proposal of adequate strategies.