The purpose of the study was to establish and quantify the minimal important change (MIC) value necessary to determine gains or losses in clinical reasoning during student fieldwork assignments as measured by the Self-Assessment of Clinical Reasoning in Occupational Therapy (SA-CROT). This multicenter prospective longitudinal study was conducted with students on their occupational therapy fieldwork in Japan. Two anchor-based methods were used to estimate the MIC values: a receiver operating characteristic-based method and a predictive modeling-based method. The MIC was adjusted based on the percentage of participants who exhibited improvement. Administered were the SA-CROT and the Global Rating of Change (GRC) scale as an anchor. A total of 111 students from 11 occupational therapy educational programs in Japan responded (response rate 29%). Overall, there was a significant difference (p < 0.001, effect size was r = 0.80) in SA-CROT before and after fieldwork, and 81% of students showed improvement in the GRC scale. The adjusted MIC value was 3.69, with 95% confidence interval of 2.29-4.97. This anchor-based, adjusted MIC value is the most reliable value to interpret the changes in SA-CROT before and after fieldwork. The SA-CROT's MIC value can be used as a cut-off point from a learner-centered perspective when considering educational methods and environments in fieldwork.