The purpose of this paper is to describe and analyze the process of construction of meaning about the shape of the Earth and the alternation of day and night, which is inherent to the practice of experimental science teaching. This teaching practice was gradually done by the researcher in a 1st grade class of a Portuguese primary school. The class was composed of 18 students, ten girls and eight boys, with ages ranging from six to seven years old. The analysis of the meaning construction process focused on the class diary prepared by the researcher, based on the field notes and audio recordings made during the participant observation in the classroom. The goals of the interpretive analysis of the diary were as follows: a) identifying the students' initial ideas expressed during class about the shape of the Earth, b) characterizing the processes that promote the construction of knowledge about the topics under study; c) and presenting the learning that takes place during class. These instances of learning described in the class diary, combined with the results of a true or false questionnaire, suggest that most students developed a good understanding about the shape of the Earth and the alternation of day and night.