Science education is crucial for fostering knowledge across academic disciplines. Past efforts to enhance science achievement at the elementary level have explored various instructional strategies. Among these, the Understanding by Design (UbD) model has shown notable potential in improving science achievement outcomes compared to traditional methods. This quasi-experimental study investigates the impact of the UbD model on the science achievement of fifth-grade students in Pakistan. Using a pretest-posttest design, students were randomly assigned to either a control group or an experimental group. The academic achievement science test (AAST) was administered to measure outcomes. Data analysis, incorporating independent sample t-tests and mixed between-within subject ANOVA, indicated that the UbD model significantly improved science achievement over conventional teaching methods. These findings underscore the effectiveness of UbD in science education and highlight the importance of innovative pedagogical strategies for promoting academic success among elementary students. Implications and future research directions are suggested.