The key aim of the present study is to examine the contribution of Lesson Study in the context of collaborative planning of teaching, aiming at the students’ learning attainment. The qualitative research held from February 12th to April 1st 2016, took place in the second class of a high school, in Attica and 31 students in total participated. It concludes that Lesson Study detailed planning, sincere and effective cooperation of teachers with mutual respect, togetherness and fellowship, are fundamental elements for success. In addition, the study pinpointed the important contribution of the teamwork teaching method to students’ learning, which was developed in the context of Lesson Study. The understanding of the research lesson by the majority of students and their positive attitude to future implementation is an important finding of the survey. Instead, a minor percentage of students remained neutral. Almost total participation of students in teaching and their answers to individual and group worksheets showed their better understanding of knowledge.