GeoGebra-Supported Instruction and Students' Trigonometry Performance in Ghanaian Senior High Schools: Evidence from a Quasi-Experimental Study

Weak conceptual and representational understanding of trigonometry remains a persistent challenge in secondary mathematics, especially where instruction emphasises formula recall rather than coordinated reasoning across diagrams, ratios, tables, graphs and contextual problems. This study examined whether GeoGebra-supported instruction was associated with higher Senior High School students' trigonometry performance in Ghana than conventional teacher-centred instruction. A quasi-experimental pre-test and post-test non-equivalent control group design was used with 80 SHS2 students from two schools in the Bono Region. The GeoGebra group received five days of teacher-orchestrated, student-active instruction involving dynamic manipulation, visualisation, representation-linking and guided inquiry, while the comparison group received conventional instruction on the same content over the same period. Baseline scores did not differ significantly between the groups, t(78) = 0.03, p = .977. The primary intervention effect was examined using regression/ANCOVA with post-test score as the outcome, instructional group as the predictor and pre-test score as the covariate. After controlling for pre-test performance, GeoGebra-supported instruction predicted significantly higher post-test scores, B = 33.31, 95% CI [29.71, 36.90], p < .001; the adjusted model explained 81.5% of the variance in post-test performance. Welch's t-test and Mann-Whitney U sensitivity analyses supported the same conclusion. Learner perceptions were moderately favourable but not significantly above the agreement benchmark. The findings suggest that GeoGebra may support trigonometry performance when embedded in guided, representation-rich pedagogy, although the short intervention, intact-class design and very large effect require cautious interpretation.