<![CDATA[This study aimed to describe the profile of addition and subtraction performance and to examine the effectiveness of SIGMA-ToSM in improving arithmetic fluency of a slow learner student. The study employed a Single Subject Research design with an A-B-A pattern involving baseline-1, intervention, and baseline-2 phases. The participant was one grade VIII student at SMP Negeri 2 Cimerak who had been identified as a slow learner through teacher interviews, initial arithmetic testing, and psychological assessment with an IQ score of 73. Data were collected through repeated administration of the Test of Second Mathematics (ToSM) as the assessment instrument, SIGMA-ToSM as the structured intervention instrument, observation, interview, and documentation. The main indicator was Operations per Minute (OPM), representing accuracy and speed simultaneously. The findings showed that the mean addition score increased from 4.66 OPM in baseline-1 to 22.54 OPM during intervention and to 30.34 OPM in baseline-2. The mean subtraction score increased from 4.26 OPM to 14.37 OPM and then to 20.13 OPM. Visual analysis showed positive trends, stable maintenance at baseline-2, positive level changes, and 0% overlap between compared conditions. Observation and interview data also indicated better readiness, engagement, strategy use, independence, and confidence. These findings indicate that SIGMA-ToSM was effective in improving addition and subtraction performance of the slow learner participant, with stronger effects on addition than on subtraction.]]>
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