This paper depicts the different paths followed by two teachers in the development of their professionalism, through their participation to a pilot group experimenting a fairly innovative teaching approach, inspired to Wiggins & McTighe's "Understanding by design (UbD)" methodology (Wiggins & McTighe, 1998; McTighe & Wiggins, 1999; Wiggins & McTighe, 2007). UbD is a constructivist way to organize teaching, involving significant changes to usual teaching practices. The project is part of a wider school improvement strategy actually taking place in a group of Swiss vocational schools (Ostinelli, 2007, 2008a), whereby teachers are supported by some School Improvement Advisor/researchers (SIA). The SIA can be roughly described as a figure being at the same time an advisor, a researcher and a critical friend. The key idea is, after the creation of some pilot groups, to "aggregate" other teachers and to disseminate the experience to other schools: the present article deals with the first, embryonic stage. In today's world, is quite important for teachers not only to accompany, but also to be able to prevent the change taking place inside schools; in this context, an evolution in their teaching practices is decisive. UbD can be a good path to follow in this journey, but, like various innovations, can be also difficult, either for the teacher and the SIA. This article will try to explain why one of the teachers assimilated the new methodology, improving his professionalism, while the other didn't. Why and how, in some circumstances, a lack of understanding of the situa- tion experienced can drive to negative consequences to the development of innovative teaching skills? Which is the role of motivation in this context? In order to try to give some answers to these questions, both teachers were firstly interviewed, and then a motivational test was administered to them. The collected informations proved useful for a better understanding of the dynamics underlying the described experience.
