This paper explores the education of prospective teachers with regard to the Theory of Didactical Situations when they engage in lesson study. We particularly focus on studying how a lesson study process oriented towards the Theory of Didactical Situations contributes to increasing prospective teachers' self-efficacy to plan and teach lessons based on such theory, reducing the gap between theory and practice. Prior to the study, we will discuss how the theoretical postulates assumed in lesson study affect crucial aspects of the process. The study is implemented with 47 prospective early childhood education teachers. We also consider another group of 47 prospective teachers that were engaged in practicum at the time the lesson study process took place. Using a quasi-experimental methodology based on a questionnaire developed ad hoc that captures the particularities of the didactic paradigm assumed, the results of our study show that both lesson study and practicum lead to a statistically significant increase in future teachers' self-efficacy to plan and teach lessons in line with the paradigm assumed. However, size effect measures show that the increase observed in the lesson study group is significantly higher, which supports the benefits of lesson study in initial teacher education. We discuss what the features of lesson study are that could be related to this increase. Finally, we sketch new lines of research connected with the benefits of lesson study versus other teacher education experiences like practicum, as well as with links between self-efficacy and knowledge growth in lesson study.