Abstract

This quasi-experimental study investigated the effects of Guided Inquiry-Based Instruction (GIBI) assisted by Variation Theory (GIBI-VT) on the achievement and goal orientations of grade ten students in solid geometry. Participants (N=102) from Debre Tabor City, Ethiopia, were randomly assigned to: Experimental Group 1 (EG1, n = 31) receiving GIBI-VT, Experimental Group 2 (EG2, n = 39) receiving GIBI alone, and a Control Group (CG, n = 32) receiving the traditional teaching method (TTM). Quantitative data were collected using a validated mathematics achievement test and goal orientation questionnaire. The ANCOVA revealed statistically significant differences in mathematics achievement post-test scores. Additionally, the pairwise comparisons showed that both EG1 and EG2 significantly outperformed the CG. Moreover, MANOVA indicated EG1 scored significantly higher on mastery goals orientation than EG2 and CG. Finally, the regression analysis model revealed that student's gender, Performance-Approach Post-Test Scores (PApPostTS), GIBI-VT vs. TTM, and GIBI alone vs. TTM significantly explained 47.0% of the variance in their Mathematics Achievement Post-Test Scores (MAPostTS). The GIBI-VT is an effective strategy for enhancing students’ achievement and mastery goals orientation in solid geometry. The study recommends incorporating GIBI-VT into teacher training and curricula to address persistent challenges in geometry learning in Ethiopia and similar contexts