As experimental activity takes care an important place in Physics classes, the teacher must use strategies which allow students to build up their own knowledge. In spite of it has the potential to contribute greatly to conceptual, proceduraland attitudinal aspects, lot of investigations agree that it does not occur. So, it is necessary to review them doing adequate changes in order to solve this inconvenient. In the frame of an investigation work it is proposed the application of a strategy in Physics lab works with secondary students framed in constructive and active learning, where they do a previous task, which includes conceptual, procedural and attitudinal aspects. The methodology used is the comparison of groups, one the control group (CG) and the other the experimental one (EG). The CG will develop the activities in a traditional way and the EG will use the conductivity strategy. Pre tests, which will be used as one of the instruments for dates collecting, allow students prior ideas arise. Here we present a model of a pre test referred to the lab experience: The transformation of electric energy in thermic one