The Theory of Evolution (TE) is the backbone of biology and is the best way to explain the diversity of species that exist on the planet. However, despite all the supporting evidence, TE remains poorly understood and accepted. In this study, the levels of acceptance and understanding of TE were measured, respectively, using the Inventory of Student Evolution Acceptance (I-SEA) and Knowledge of Evolution Exam (KEE) questionnaires, in high school students in Monterrey, Mexico (N = 370). The results show that the acceptance of TE ranges from moderate (90.3 out of 120) to high (3.7 out of 5), depending on the scale with which it is measured, while the level of comprehension is low (4.5 out of 10). Statistical analysis of the data collected reveals that there is a positive relationship between acceptance and understanding of TE (r = 0.34). In addition, the proportions of I-SEA and KEE were evaluated based on several factors, such as religion and educational level of the parents, among others. It was found that the level of education of the parents positively affects the understanding of the basic concepts of TE, while religion is the main factor of negative influence on both acceptance and understanding. Finally, the low comprehension shown in this study suggests a revision and readjustment of the contents that are taught in the upper secondary education curriculum.