This paper provides evidence on the differences among Spanish regions, regardless of other factors, in student achievement -- in Language, Mathematics, Science and Citizenship -- of fourth graders. This is the first paper in Spain that analyses these differences for Primary Education in all Spanish autonomous communities. The data in the Spanish General Diagnostic Assessment of 2009, by means of descriptive analyses and estimation of multilevel regressions, led us to show that, beyond differences between and within schools, variation in student achievement in Spain is even larger between regions than schools. Furthermore, regions with a co-official language produce worse results than others, especially in Science.