This article derives from a doctoral thesis work. The aim of it was to characterize the processes of negotiation of meaning in Physics classes at High School in the Energy topic. The investigation adopts ethnographic characteristics. In particular it is a multicases study. Each case was conformed by the set of all the classes in which the Energy topic was studied. The four cases studied are considered instruments to analyze the processes of negotiation of meaning. The corpus is made up, mainly, by the audio of the communicative interchanges that occurs in the classes. Interviews with teachers were made and notes of field from the presence of the investigators in all the classes were registered. For the transcription and the analysis of the interchanges some elements of the Conversational Analysis were used. In this paper the construction of indicators is discussed to represent the communicative interaction between the professor, the students and the content. Also, the criteria are put to consideration that has allowed to determine negotiation degrees.