An educational path on relativistic dynamics has been designed and experimented in an upper-secondary school class to introduce essential concepts for making meaning of mass-energy equivalence. The pathway aims at building conceptual understanding of relativistic linear momentum, kinetic energy and their interrelation. It draws on relativistic invariant quantities and exploits thought experiments as well as educationally relevant ones; it illustrates both scientific modeling by induction both hypothetical-deductive methods for assuring logical consistency. Rough new technologies were used: an on-line simulation of light-clock and timed animations of two-particle relativistic collision. Learning and understanding were assessed by both comparing the administered pre- and post-test both analyzing the latter. General interpretive questions were asked during the teaching/learning process in order to find out pupils' intermediate explanatory models and problem solving skills in similar contexts. An analysis of the interplay among prior, posterior and intermediate answers is presented here. The results indicate conceptual change for kinetic energy and vacuum light-speed. Only understanding of time interval dilation effect was detected instead.