In this article, we review some of the ways socioeconomic status has been measured on assessments and the issues associated with measuring SES of students, issues which are not limited to statistical concerns. We also present possible proxy measures that could be used as a means of potentially overcoming some of the problems with current measures of SES. Any proposed measures would need to be tested for validity and reliability so we also present elements for a study assessing the construct validity of aggregate measures of SES as proxies for student SES on assessments. We use NAEP and TIMSS as examples, however, these approaches could be applied to other assessments and research contexts. (Contains 1 figure.)