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, [S. l.], v. 3, n. 1, p. 35–49, 2026. DOI: 10.66993/ijhedcs13457202635-49. Disponível em: https://journals.iempsglobal.org/index.php/IJHEDCS/article/view/457. Acesso em: 5 aug. 2026.