At primary school in which scientific disciplines are still a horizon, scientific education cannot be similar with the middle or secondary school ones. First, epistemological reference to sciences must be thought not only about knowledge but also about practices ; secondly, the psychological conception of scientific objectivation must consider continuity between the three "worlds" - internal, physical and social - of thinking and the intermediary role performed by signs; finally, it is necessary to consider the interconnection of the scientific curriculum with other ones as well as the multiplicity of references, aims and possible construction at primary school. It is therefore a question of specifying characteristics, dynamics and relations of mainly scientific times in the flux of school times. We propose to think curriculum as a group of school times with scientific aims linked up with other times by relations of cohesion and coherence: cohesion is what allows to assure a relation of continuity between two different times while coherence is what allows group of distinct times to contribute to the same aim. The dynamic of every time with scientific aims is grounded on two processes: "objectification", and "objectivation". The objectification achieved by teachers leads, from different possibilities or references, to material and symbolic objects which can be afforded by pupils. The objectivation achieved in most cases by pupils leads to different elaborations from both objects and linked tasks. We make it clear that this curricular elaboration offers opportunities to understand scientific education at primary school. Putting object, sign and work side by side allows to conceive dynamic contents of school times - contents which are changed during an empirical and dialogical activity. Moreover, the capacity to manage the relations of cohesion and coherence between these times and within a broader curricular network appears to be one of the main components to define a speciality for primary school teachers.
