Modelling in Science teaching is considered an important learning process and content of educational research as well. In the present work, a classification of the models which appear in literature is initially presented. In particular, the models have been classified in four classes related to the visual effect of the model and in four other classes related to the syntax-creation of the model. In addition, the "Modelling Layer" (primary, secondary, tertiary) depending on the given data at the beginning of the model construction has been introduced and defined. At the primary layer, the only given data is the modelling object, that is the system (or phenomenon or procedure) which is being studied. At the secondary layer, the theoretical analysis of the model, that is the correlations between the concerned magnitudes, is additionally given. Finally, at the tertiary layer, the study of the model takes place, in order to conclude about the system that is being studied.