Sunday, Yomi, Salami Dharriyat, Olorunnishola Olufikayo Agnes, & Shuaibu Kennedy. " Development and Assessment of Upper Basic Students’ Conceptual Understanding of Mathematics Knowledge Using Two-Tier Diagnostic Test in Kogi State, Nigeria." NIU Journal of Educational Research [Online], 12.2 (2026): 47-62. Web. 24 Jun. 2026