In educational assessment research, aberrant responses are often treated as outliers that threaten the reliability and validity of measurement instruments. However, we argue that combining Rasch-based person-fit statistics with structured qualitative item analysis can enhance the interpretability of test scores and illuminate patterns of instructional alignment. This study proposes a methodological framework for identifying structural patterns associated with students’ unexpected performance in a national mathematics examination. Our guiding assumption is that certain patterns of aberrant responding may be consistent with washback mechanisms associated with high-stakes examinations. Using data from the National Level Examination in Mathematics for Grade 9 in Latvia (N = 17,962), we applied Rasch-based fit statistics and qualitative item analysis to construct instability, understanding, and drill indices. The findings suggest that aberrant response patterns can provide insight into students’ learning behaviors at both individual and school levels. In some institutional contexts, these patterns may reflect a stronger emphasis on exam-focused preparation relative to conceptual learning.