Professional training, as a part of professional development should cause changes in the knowledge and skills of teachers, that in turn cause changes in teaching and improvements in students' learning. Therefore, the aim of the thesis was to determine changes in the teaching methods that biology teachers are making as they are professionally developing through professional training, which includes experts' and application of learning, critical analysis and self-reflection. The changes were monitored and ascertained by a (self)analysis of nine videos of class sessions in accordance to the protocol, and the paper comprehends three teachers. Nine videos were analysed, three videos of each teacher. The initial video analysis established a common practice which determined the aspects for improvement of the individual teacher. The analysis of the second video reflects the changes that the teachers have experienced after the professional meeting when they have implemented what they had learned into their teaching practice (this method is the first level of support).The analysis of the third video reflects the changes caused by the second level of support, namely teaching in accordance with expert preparations and continuous participations in learning communities during which they were exposed to critical analysis and self-reflection on the lesson. The analysis showed positive changes in teaching. The first level of support did not improve those aspects that require a change in students, such as free presentations of ideas and clarification requests, as well as taking notes. These aspects required the second level of support. The aspects that are part of the formative evaluation have improved in relation to the appearance in the initial lesson, but are still not sufficiently represented. The entire professional training improved the recognition of teachers' needs for their own professional development and directed them toward planning one.