This article deals with the debate on the assessment of pupils' socioeconomic dispersion among schools. First, the paper complements the traditional way of measuring "segregation," which refers to the distribution of a specific subgroup of pupils across different schools, by introducing a new measure which we call "school polarization level." As argued here, "school segregation" and "school polarization" are associated with different phenomena and so point to different problems with different policy implications. Second, the paper illustrates the application of such measures for the cases of 10 Catalan municipalities (Spain) that apply different policies of school assignment based on residence (school zoning). (Contains 4 tables, 4 figures, and 6 notes.)