Self-efficacy affects the students’ perceptions of their own competence in mathematics. The learning environment can influence the student's self-efficacy, but also the experiences of meaningful learning. This study examined changes in mathematical self-efficacy in Finnish 6th-grade students through six lesson study processes. Research aimed to answer the questions: “How did students’ self-efficacy develop in mathematics learning?”, “How did the elements of meaningful learning appear in students’ learning experiences? and “What kind of learning environment does support meaningful learning in mathematics?” Qualitive content analysis concentrated on the analysis of changes in self-efficacy in surveys and themed interviews. Most changes happened in the self-efficacy sources of vicarious learning and social persuasion. The changes showed that when a student received cognitive and social support for learning through group work and also continuous feedback from teacher student's mathematical self-efficacy strengthened. This produced meaningful learning experiences which can be considered when designing meaningful learning environment.