This article examines the didactic suitability of introducing models at an intermediate (i.e. mesoscopic) scale in teaching certain subjects, at an early stage. The design and evaluation of two short sequences based on this rationale will be outlined: one bears on propulsion by solid friction, the other on fluid statics in the presence of gravity. Both concern students in the first university year and were designed with common conceptions of students on these topics as a guide. The common points and the differences of the two sequences are discussed, and particularly the characteristics of the mesoscopic approach. The evaluation is made by analysing the recordings of class discussions and comparing the results of control groups via written questionnaires. Teachers' reactions have also been documented. These elements show that the proposed mesoscopic models encourage a more articulated reasoning on the physical situation, helping students to reconcile a global description with the analysis of local interactions.