This paper investigates physics teacher class planning and its consequences during implementation in class mainly focusing the contradictions emerged among teacher’s and students’ expectations of the class. This situation is analysed from a socio-cultural-historical point of view mainly supported by Activity Theory. We highlight the components of the activity and the context in which they are reorganized exploring the complexity of the dialogical classroom situation. Through the use of video recordings of an experimental task we showed students measuring and isolating relevant variables to characterize a simple pendulum. We point out important aspects of the different moments of a teacher's planning, organization and the importance of dialogic interaction in the classroom to overcome lack of communication.