Preliminary studies established that a proper set of activities lead to gain a formal mental structure (according to Jean Piaget) is helpful to understand sciences. The objective of this investigation is to evaluate the influence of the application of PEACYT’s tools (Proyecto Esquema de Aprendizaje Científico y Tecnológico) in the mental structure of high schools students. Lawson’s modified and standardized test has been applied to a sample group of students that received their classes with PEACYT’s methodology during the last three years and controls group that received their class in the traditional way during the same time. The amount of students that reached the formal structure, concrete structure and in transition between the structure have been determined and compared in both group. After the analysis of statistical test of variance analysis and Student test it can concluded that are a significance difference between this two group. The concrete mental structure has been maintained by students who received their classes in the traditional way even after three approve the high school, while other students that received their classes using PEACYT’s methodology tools have more percent of students in the formal mental structure and in average is in transition between both structure. This allows us to said that this kind of activities is helpful to achieve the formal structure from concrete structure and we recommend the PEACYT methodology in the classes at high school.