The understanding of teachers’ thought and action can be approached from several perspectives, teaching modelisation being one of them. Schoenfeld (1998b) argues that a good comprehension of the cognitions (beliefs, goals and knowledge) underlying teachers’ decisions and actions can provide a coherent and detailed explanation of what teachers do and why they do it. The research presented here is based on the implementation of a Modelisation Instrument (MI) (Monteiro, 2006; and Monteiro et al., 2007, 2008a), adapted from studies by Schank and Abelson (1977), Shulman (1986b, 1987), Santos (1991), Porlán (1993), Carrillo (1998), Schoenfeld(1998a,b, 2000a), Aguirre and Speer (1999), Sherin et al. (2000), Schoenfeld et al. (2000), Zimmerlin and Nelson (2000), Verloop et al. (2001), Climent (2002) and Cañal (2004). This chapter presents the teaching modelisation of a natural science teacher using the MI. A wide variety of scripts, routines and improvisations are detailed on the topic of Plant Diversity. However, amongst the several theoretical entities mentioned above (scripts, routines and improvisations), scripts will be given special treatment for their direct dependence onthe natural sciences subject matter, on the one hand and their capacity to became tools for reflection by science teachers, on the other hand,Teachers’ awareness that certain beliefs, goals and knowledge underpin their actual actions in the classroom, is of crucial importance to their reflection on their practice and,consequently, to improving their teaching. To this end, we present various tree diagrams which we feel provide insight into the relationships between teachers’ beliefs and actions which emerge from the scripts. These could represent a good resource in science teachers’ professional development programs.