This work presents partial results of the research "Construction of a training proposal in natural sciences oriented from the content didactic knowledge (CDC, in Spanish, Conocimiento Didáctico del Contenido), directed to teachers in their initial training from the Early Childhood Education Degree from the National Pedagogical University", specifically as it is related with the characterization of the components of CDC: the educational purposes of Natural Sciences and Natural Sciences disciplinary content taught in school, with two teachers in their initial training in science teaching internship.Given the nature of this Congress, results about Biology teaching are preferred, from which we identified the high degree of significance that the contents related to the living things (mainly plants and animals) have, not just for training teachers but also for children and the relationships with teaching practices and strategies focused on the observation and experimentation, which are also assumed as purposes of natural science teaching.