Large-scale international studies focus most of their efforts on measuring knowledge as academic achievement. For this reason, more attitudinal instruments, such as questionnaires for students, teachers, and principals, are left in an instead auxiliary role. In the case of the International Civic and Citizenship Education Study (ICCS) 2009, in addition to measuring civic knowledge as academic achievement, a series of relevant instruments are considered within the concept of citizenship, aimed at measuring attitudes, beliefs, and behaviours. To encourage the use of the ICCS database incorporates’ variables built based on composite indices (estimated with Item Response Theory [IRT]) of those scales that address the same issue, such as trust in institutions, participation, school climate, attitudes towards ethnic minorities, among others. Frequently ICCS’s variables are used as they come in the database without stopping to analyse or problematize the validity of these measurements and their consequences in terms of contrasting hypotheses. Using the scale of attitudes towards equal rights between men and women, this chapter begins by describing, in general terms, the characteristics of ICCS and then moves on to factor analyses that show the possible validity problems that can arise from the use of the scores proposed by ICCS. The conclusions address the implications in terms of validity.