Developing metacognition in students is essential for fostering critical thinking in school. One of the skills necessary to achieve this goal is the cultivation of metacognitive vigilance--a potential means to regulate some ways of thinking held by individuals. Of particular importance is essentialism, as it underlies discourses such as racism and also hinders the comprehension of various biological models. In this paper, we aim to characterize the metacognitive regulations on essentialism made by high school students from Buenos Aires, Argentina. This exploration occurred within the context of a didactic sequence on the relationship between biology and human races, designed to promote metacognitive vigilance. Employing a qualitative approach, various types of metacognitive reflections were identified. These reflections reveal that some of the students consciously identified instances of essentialism in their daily lives, assessed its legitimacy, and constructed alternative explanations by drawing from biological models. These findings underscore the importance of nurturing metacognition as a means to deconstruct hegemonic and common-sense discourses, including those rooted in racism.