The present study aimed to construct and standardize a Test of Mathematics Achievement (TMA) for Class VIII students to ensure a valid and reliable measurement of mathematical proficiency. The tool was developed following a systematic process that included content selection from the Mizoram Board of School Education (MBSE) syllabus, item construction based on Bloom’s taxonomy, and expert validation. The TMA initially contained 35 multiple-choice items, which were piloted and analysed for item difficulty and discrimination. Following item analysis, 30 items meeting acceptable psychometric standards were retained. Reliability was established using the split-half and Kuder–Richardson (K-R 20) methods, yielding coefficients of 0.78 and 0.79, respectively, indicating high internal consistency. Content and construct validity were verified through expert judgment and theoretical alignment. The standardized TMA thus provides an effective tool for assessing mathematics achievement, facilitating pedagogical improvements, and supporting evidence-based educational practices, particularly in culturally responsive and ethnomathematical contexts.