[eng] A comprehensive current educational innovation aims to teach 21st-century skills, which invariably include critical thinking (CT). The implementation of CT requires some mastery of its constituent abilities and also holding the dispositions and attitudes that are necessary for its adequate enactment. The literature on CT attitude measurement uses one main measurement tool, which is very long and only applicable to adults. In order to include young people in this study, a new short and viable tool was designed to assess CT attitudes and analyze its psychometric properties. The design was carried out through a two-stage process that involved convenience samples made up of primary and secondary students from twenty different schools, who answered the developing instruments and whose data are analyzed through a polychoric correlation model. Confirmatory factor analysis reported optimal goodness-of-fit indexes for a six-factor structure of the instrument: confidence on reasoning, truth-seeking, open-mindedness, curiosity, system and prudence-analysis. The matrices of standardized coefficients and correlations between constructs provide evidence of convergent and discriminant validity for the six-factor model, which also attained good reliability indices. These psychometric results provide empirical support to the validity and reliability of the instrument's six-factor theoretical model, which allows the evaluation of young students' CT attitudes. Finally, the instrument's role in facilitating the educational interventions to foster CT learning from the educational elementary stages and the development of future research is discussed.