This chronicle of experience presents the transformations in the teaching practice of a natural sciences teacher in initial training through the implementation of the Lesson Study methodology, aimed at strengthening scientific thinking skills through the development of practical experiences in the science laboratory of the Departmental Rural Educational Institution La Fuente, with students from sixth to eleventh grades. The study has a qualitative approach and an action -research design. Three cycles of reflection were carried out, based on the assessment processes among academic peers, analyzing the constitutive actions of the teaching practice: planning, implementation, evaluation and reflection. Among the most significant preliminary findings, it is highlighted that the trainee teacher performs coherent exercises of curricular descent from the macro to the micro level; also, he/she is able to differentiate an audiovisual evidence from a learning evidence, reflected in his/her discourse and planning. However, the teacher in his exercise favors the student -knowledge relationship, leaving aside the role of mediator in the process and the greatest difficulty he presents in his teaching practice corresponds to the classroom management during the development of the laboratories. In order to remedy these problems, the teacher, in a self -reflective manner, suggests making substantive modifications to the proposed learning activities, based on the feedback given by his peers with the purpose of permanently improving his teaching practice in the classroom. In summary, the implementation of the Lesson Study methodology generates actions of professionalization of the teaching practice, where teachers investigate, reflect and transform their teaching practice in the classroom, with the purpose of permanently improving it.