The paper is about a study that investigated how the integration of assessment for learning enhances learning achievement among secondary school biology students in Tanzania. A quasi-experimental design involving pre-test and post-test of non-equivalent control and experimental groups was used to ascertain how the integration of assessment for learning into teaching and learning processes enhances students' learning achievement. Two boarding secondary schools located in the suburbs of Dar Es Salaam were selected. Students in the two schools had maintained equivalent performances in national examinations in previous years. The results showed that the students taught using teaching and learning processes integrating assessment for learning outperformed those taught using conventional approaches. The integration of assessment for learning is likely to have contributed to the higher learning achievement in the experimental group. The study contributes to our understanding of how teachers in resource-constrained classrooms can integrate assessment for learning techniques into their day-to-day lessons, thereby harnessing the power of assessment to enhance learning and raise standards.