The paper reports how a teacher and her students use drawings as a resource for observations and how such observations are connected to different epistemic practices in science lessons. Interactional data in a 1st grade classroom were analyzed based on Ethnography in Education. Results show that the use of drawings materialized children's transition process from sheer imagination to recording observations. Such transition reveals observation as more than simply introducing children to sensorial experiences or based in classical empiricism when other epistemic practices are considered. These practices emerged from the engagement of students in observations. Observing in science lessons was a tool for revising/refining a model and assess the merits of the model, in addition to serving as a source to present arguments and construct rebuttal. Finally, the observation itself was not given as something neutral or immune to debate. The same observation became a reason for disagreement among peers, which generated communicative demands for persuasion between them. Finally, implications towards research and pedagogical practice with children are also discussed.