At present, the teaching of algebra in primary education in the Peruvian context is under an arithmetic approach, which restricts the student to make new forms of reasoning where variables, alphanumeric symbols, and general rules can intervene to respond to various problematic situations. In this sense, the objective is to evaluate the effect of the instruction model of Merrill on the development of algebraic thinking compared to those that had conventional learning. The approach is quantitative, with a quasi-experimental design, with two control groups and two experimental groups. The study population consists of 82 students in the third grade of primary school, corresponding to two public institutions. Likewise, a questionnaire of ten items based on two dimensions of generalized arithmetic and functional thinking was applied, supported by the model of Merrill, which proves that there are significant differences between the pretest and posttest, resulting in effective and reaching an average of 13, 25 up to the intermediate level of algebrization. The finding revolves around creating a path where this traditional instruction can move to functional thinking demonstrated by the response capacity of students, in addition to the combination of algebraic contents with digital resources.