The Chemistry Teaching-Learning Sequences (SEAqs) designed by the students of the Master of Secondary Science Teacher Training (PCFI) are analyzed. The question of the study is: In what way do the activities in the SEAqs designed by PCFI students promote modeling? Based on the legitimation code theory and the perspective of the school scientific activity, a theoretical-methodological tool of a semantic and cognitive nature is proposed for the characterization of 20 SEAqs through content analysis. The conclusions point to the difficulties that PCFI students have when designing SEAqs that promote modeling, as well as to the value of the theoretical-methodological tool which was used to illuminate these difficulties for the teaching of both chemistry and science in general.