With each survey cycle, the measurement of socio-economic status in PISA must strike a delicate balance between at-times conflicting goals: accuracy, coverage, cost-efficiency, trend continuity, relevance (keeping up with changes in society) and comparability across countries. Over the past decade, a number of changes were introduced in the instruments and scaling processes; new related questions were added; and experiments were conducted with alternative question formats. In light of these changes, new variables, and experiments, we examine the quality of the indicators and scales that contribute to the index of economic, social and cultural status (ESCS) in PISA. We conclude with implications for questionnaire development, recommendations for scaling, and suggestions for future research.