This paper presents Excale – Math, a national assessment conducted on representative samples of students from different grades in Mexico since 2005. The purpose of this assessment, designed, applied and analyzed by the Instituto Nacional para la Evaluación de la Educación (National Education Assessment Institute, INEE), is to provide a global overview  of academic achievement at the primary and secondary education levels. Excale assessments have three fundamental characteristics that address its purpose: they are criterion-referenced, reflect the national curriculum, and have a matrix design. Following a brief description of its application schedule, comments are offered on the design of the assessment, and some general results of recent applications (preschooler, third, sixth and ninth grades) are shown.