Abstract
The principle of double stimulation is foundational within Cultural Historical Activity Theory. This paper illustrates an analysis of the model of double stimulation applied to a Change Laboratory in an Italian vocational school. Results show that the four phases relating to Apparatus 1 do not follow the model in strict order, nor do they become concentrated in single sessions. The analysis points at quantitative and qualitative differences of the four phases between the first block and the second block of sessions, with the sixth session acting as a boundary.