Hands-on and minds-on activities about teaching and learning the concept of energy in primary school will be presented.The word “energy”, even if already used by the children in everyday life, is not cited by the teacher during the lessons of the didactic path in order to build the underlying concept on scientific bases, unfolding all the basic aspects and avoiding misconceptions and misunderstandings. The concept of energy is constructed by starting from the cause-effect relationship and focusing on the differences of potentials (increases and decreases in potentials) of the extensive quantities involved in the process of interaction being analyzed. Subsequently, in order to lay the foundations for the concept of conservation, the relationship between potential differences and the associated extensive quantity currents is recognized, to build a (qualitative) budget law (relationships of direct or inverse proportionality): some increase in potential (effect) of an amount of an extensive quantity, at the expense of some reduction in potential (cause) of another amount of extensive quantity. The energy concept, then, arises from the identification of the “proportion” between two processes taking part in an interaction.The activities and the didactic materials experimented in a 5th grade classroom will be presented. Moreover, in order to evaluate the pupils’ progresses in the development of the concept of energy, linguistic criteria to analyze worksheets and conversations will be introduced together with some results which highlight evidence how children express their thoughts using “signs” that the teacher can then use to create a link between the concrete experiential plane and the conceptual one.