<p>This study explored the impact of peer assessment strategies on students’ academic achievement and retention of Biology concepts. Using a 3 × 2 factorial research design, the study involved 138 SS1 students from three intact classes. Data were collected through the Biology Achievement Test (BAT) and the Biology Retention Test (BRT). In the experimental groups, students were taught Biology topics and assessed using peer assessment strategies, while the control group received the same instruction but was evaluated by the teacher. Descriptive statistics, including mean and standard deviation, were used to answer the research questions, while an analysis of covariance (ANCOVA) was conducted to test the hypotheses. The findings revealed that students assessed through peer assessment strategies performed better than those evaluated using traditional teacher-based methods. Among the peer assessment strategies, intra-group peer assessment was the most effective. Additionally, students taught and assessed using peer assessment demonstrated higher retention rates, with intra-group peer assessment proving to be the most beneficial approach. A significant difference was observed in the mean achievement scores between students assessed through peer assessment and those evaluated by teachers. These results highlight the effectiveness of peer assessment strategies in both teaching and evaluating Biology students.</p>