Teaching practices, due to their contextual nature and particular form of implementation, can favor or limit learning in the school context. From this perspective, a case study is designed that delves into the content of the reflection about the teaching practice of a biology teacher in service. To this end, the teacher makes a critical observation of his practice, commenting on all those teaching situations that concern him. Each commented observation was deepened through a focused interview. The information from the commented observations and focused interviews was analyzed with the Atlas-ti 8.0 software. This revealed teaching concerns regarding education, consequences and implications for student learning and two teaching difficulties in Biology, which were: the use of questions and the teaching explanation. The scope of reflection as a source of professional knowledge is discussed
