Background: It is generally accepted that well-established classroom rules prevent problem behaviour, while also supporting students' achievement gains. Yet, there might be considerable variability in students' underlying motives to comply or refrain from complying with classroom rules, with some students adhering to them because they fully accept them as their own, and others feeling compelled by external or internal demands to do so or even defying the rules altogether. Aims: Grounded in self-determination theory, this study aimed to examine whether students' reasons for following (i.e., internalization) and for refraining from following (i.e., defiance) classroom rules differentially and uniquely predict student outcomes, including feelings of resentment, acting out, cheating, and truancy. Sample: A total of 1006 students (46.7% boys; M = 14.18 years ± 1.73) out of 56 different secondary school classes participated in the study. Methods: Students were invited to fill out an online survey about experiences with their head teacher. Results: For three out of four outcomes, identified regulation and external regulation to follow classroom rules were found to be, respectively, negatively and positively related, whereas a null relationship with introjected rule following was found. Controlled non-rule following was most strongly predictive of maladaptive functioning, as indexed by more feelings of resentment, acting out, cheating, and truancy. Conclusions: Whereas students' ownership of rules is critical to prevent classroom misbehaviour, their pressured non-adherence is a risk factor.