The aim of this study is to investigate and explain inconsistencies within the social constructions of school rules as they take shape in everyday interactions between teachers and students, and to explore how students interpret these inconsistencies. An ethnographic study is conducted in two primary schools in Sweden. According to the findings, implicit rules, i.e., unarticulated supplements or exceptions, can, at least in part, explain inconsistencies in teachers' efforts to uphold explicit school rules to the explicit rules. Nevertheless, rule inconsistency and unarticulated implicit rules appear to create rule diffusion, which, in turn, creates a prediction loss among students. They cannot always predict what will be appropriate behaviour in particular situations, and how teachers will react to their behaviour. Furthermore, this appears to result in a negotiation loss for students. They cannot openly discuss and negotiate on rules if they are unaware of such rules.