Critical thinking skills (CTS) are a group of higher order thinking abilities related with complex processes of learning like contextualization or problem solving. This exploratory research study identified whether critical thinking skills were present in high school humanities classrooms. The study was carried out in a private school in Bogotá, Colombia through qualitative methods and content analysis. The study sought to identify CTS in students' actual learning processes. Data collection techniques included classroom observations, document analysis and focus groups to identify skills in teachers and eighth grade students from a humanities-focused high school curriculum. Results demonstrated the presence of argumentation in written and oral classroom material. Analysis was also evidenced through questioning, inferencing and other exercises. Motivation was also an observable element, reflected in explicit expressions and gestures, and in the use of extra material in the classes.