This paper discusses the concept of ‘rational civic attitudes’ and its link to knowledge, using data on eighth-grade students from 38 countries in the International Association for the Evaluation of Educational Achievement International Civic and Citizenship Education Study to examine these questions: (1) Are country-averages on self-reported ‘Trust in Civic Institutions’ validly comparable across culturally and institutionally diverse countries? (2) Is the relationship between such trust and students’ Civic Knowledge contingent on the extent of corruption in their country, on how effective the government appears to be, and on standards of living, health and education? (3) Are students with better ‘Civic Knowledge’ more supportive than others of ‘Equal Rights for all Ethnic Groups’ and ‘Gender Equality’ and do they have higher ‘Expected Adult Electoral Participation’? The answer to question (1) is ‘NO’. To questions (2) and (3), the answers are ‘YES’. The findings fit the explanation that better knowledge promotes more rationally based civic attitudes.