Motivational regulations, as conceptualized by Self-Determination Theory (SDT), are fundamental for understanding engagement in diverse contexts. This study examines the structure of these regulations by exploring both their hierarchical and situational multidimensionality, with a focus on testing the Specificity Hypothesis—which posits that motivational regulations vary in situational specificity along the self-determination continuum. Specifically, it suggests that autonomous motivation is more subject-specific than controlled motivation. For instance, students may show high intrinsic motivation in one subject (e.g., mathematics) but lower levels in another (e.g., first language), whereas controlled motivation tends to be more stable across subjects. By investigating how each type of motivational regulation is structured across multiple school subjects and levels of generality, the study aims to address a largely unexplored question in SDT: how the degree of specificity differs across the regulation types and what this implies for the differentiation of motivational experiences. Multiple structural models were evaluated to determine which best capture the distinct characteristics of motivational constructs within academic settings. Two questionnaires were administered to psychology students, measuring general academic motivation and motivation toward five specific courses. Using a bootstrap resampling method, nine structural models were compared, examining both regulation construct and item structure. Results consistently support a hierarchical model with an additional item-related factor, underscoring this structure’s superiority across all types of regulation. Findings indicate substantial distinctions in situational motivational measures based on self-determination levels, supporting the Specificity Hypothesis, contributing to the refinement of SDT and establishing a foundation for future motivation research within this theoretical framework.