The following research presents the outcomes of a cohort study investigating formal thinking skills among first and second-year secondary school students. A specially crafted instrument, the Logical Thought Performance Test for Adolescents (LTP-A), was employed to gauge the level of formal thought. The LTP-A assesses various aspects, including: combinatorial reasoning; proportional reasoning; permutation; inferences derived from exclusive and inclusive disjunction; biconditional and asymmetric implication; and, modus tollens. The study compares the achievements of four student groups from two educational institutions at two distinct time points, with a thirty-year gap. The independent variables include the sociocultural level and the epochal aspect. Methodologically, one-way analysis of variance and cluster analysis were performed, showing significant differences in relation to sociocultural level. Results suggest that the sociocultural factor outweighs epochal differences. Then, a content analysis of some answers was carried out to detect resolution strategies, some conceptual categories and types of errors. Conclusions explore the moderating role of students' sociocultural levels, and provide educational recommendations.