In their situated expectancy-value theory, Eccles and Wigfield (2020) assume students' competence and value beliefs to be situation-specific and thereby to be "situative" in nature. Even though motivation research has gradually been developing an understanding of this situative nature, for instance, by disentangling time-consistent and fluctuating proportions of competence and value beliefs at the analytical level of the individual, most studies still have not disentangled them at the class level. The present study sought to close this gap by applying a multilevel modeling approach based on data from 1,617 ninth-grade students in 78 classrooms across five consecutive math lessons. Our findings revealed significant proportions of trait variance and state residual variance in students' competence beliefs, value beliefs, and their perceptions of autonomy-supportive teaching behaviors at the individual and class levels. Larger amounts of variance could be attributed to the individual level compared with the class level and to fluctuating compared with time-consistent proportions (across levels). Furthermore, students' perceptions of autonomy-supportive teaching behaviors predicted their situation-specific competence and value beliefs, whereby time-consistent differences, both between students and between classes, explained more variance than fluctuations within students and within classes. Thus, our findings supported the situative nature of competence and value beliefs but also revealed that, by and large, time-consistent differences in the perceptions of autonomy-supportive teaching behaviors between students and classes had more predictive power for students' competence and value beliefs than intraindividual and intraclass fluctuations over time.