Abstract
This quasi-experimental study evaluated the effect of structured formative assessment practices on senior secondary students’ learning outcomes in Mathematics in Ahoada-East Local Government Area, Rivers State, Nigeria. Using a pretest–posttest control-group design, 160 Senior Secondary School (SSS2) students (80 experimental, 80 control) from four purposively selected schools participated. The experimental group received a 5-week intervention in which teachers implemented systematic formative assessment strategies (frequent low-stakes quizzes, self-assessment and peer assessment). The control group received regular instruction without the structured formative assessment package. Mathematics achievement was measured using a validated researcher-designed test. Analysis of covariance (ANCOVA) controlling for pretest scores showed a statistically significant effect of the intervention on posttest achievement. The experimental group displayed substantially higher adjusted posttest means (M = 68.5, 71.4, 67.8) than the control (M = 52.3, 54.2, 53.8), Cohen’s d ≈ 1.38. Findings suggest that deliberate formative assessment practices positively affect mathematics learning outcomes at the senior secondary level. Recommendations include teacher professional development on formative assessment, integration of formative assessment in curriculum implementation, and scale-up studies across Rivers State.