Studies on critical thinking often overlook the work done by teachers in the classroom to develop this skill. However, studying critical thinking from the teacher's perspective is key to closing the gap between theory and practice. This study looks to characterize the work done by Spanish-speaking teachers in Latin America to integrate critical thinking into their practice. To do so, an online survey was sent to the participants of a Massive Open Online Course (MOOC), asking them to describe their work with critical thinking in their classroom. Responses from 278 participantes were then analysed using an exploratory sequential design. During the qualitative phase, a series of categories emerged based on the topics chosen by the teachers, the activities they proposed, and how they linked these to the development of critical thinking. The frequency with which these categories appeared in the teachers' responses was then measured during a subsequent quantitative phase. Variations in these frequencies were also analysed based on the subjects taught by the teachers and the age of the students. The results reveal that teachers primarily try to develop their students' critical thinking skills by integrating them into their subjects; not teaching them separately. Furthermore, they do so by choosing topics that help the students understand the world better from different subject-specific practices. Therefore, when implemented by teachers, critical thinking is highly dependent on the subject. These results suggest that there is a mismatch between educational practice and existing research, which tends to advocate the specific and explicit teaching of critical thinking, whether as a separate subject or through a cross-curriculum approach.