Students face difficulties in the transition between graphs representing different physical magnitudes and in the understanding of the corresponding phenomena. The present work studies the application of the mathematical concepts of slope and area in the framework of representations of the magnitudes of position, velocity and acceleration in the linear uniformly accelerated motion. This is done for two different cases, firstly by changing the reference system and secondly by changing the acceleration. Our intervention with students coming both from the theoretical and positive - technological branch was made by using an MBL system. The results show that the students coming from the theoretical branch have a better improvement according to SOLO cognitive levels than those coming from the positive - technological branch. The SOLO levels of the theoretical group students are lower than those of the other's group.