This article focuses on the results of an investigation about the "traffic light" method in kindergarten, which is used as a self-assessment method, a strategy by which the preschoolers evaluate their own progress in achieving the learning objectives, and the teacher obtains an immediate feedback regarding the level of understanding of the preschoolers during the activity. Formative assessment is the most effective because it comes from the learner's own initiative, developing its self-assessment capabilities. Self-assessment is not only a challenge for children, the teacher is also committed to the spirit of evaluation that develops and promotes children's autonomy, knowing not only what the child has to learn in the classroom, but also his own level of knowledge that he has. [This paper was presented at the TDID Doctoral Students' Conference, 14-16 May 2020.]