2026. EFFECT OF STANDARDIZED AND IMPROVISED INSTRUCTIONAL MATERIALS ON STUDENTS’ ACADEMIC ACHIEVEMENT IN ECONOMICS IN ABIA STATE, NIGERIA. INT’L JOURNAL OF HUMANITIES, ECONOMIC DEVELOPMENT AND CONTEMPORARY STUDIES. 3, 1 (Aug. 2026), 35–49. DOI:https://doi.org/10.66993/ijhedcs13457202635-49.