Didactical engineering is the design and experimentation of teaching sequences, adopting an internal mode of validation based on the comparison between a priori and a posteriori analysis within the framework of the theory of didactical situations. It includes four steps:

(i) preliminary analyses investigating the epistemological, cognitive and institutional conditions and constraints;

(ii) design and a priori analysis with particular attention paid to the identification and choice of values for the didactic variables and anticipation of their potential effect on the “students-milieu” interaction;

(iii) experimentation;

(iv) a posteriori analysis and validation of the hypotheses underlying the design