This research investigates the effect of a web-based model, named "Practicing, Reflecting, and Revising with Web-based Assessment and Test Analysis system (P2R-WATA) Assessment Literacy Development Model," on enhancing assessment knowledge and perspectives of secondary in-service teachers, and adopts a single group experimental research design. The WATA system provides teachers with personalized learning resources and situated environment to practice assembling, administering tests on-line, and appraising test-related statistical information to reflect and revise test items. The sample consisted of forty-seven secondary in-service mathematics and science teachers in a summer program for 36 h within six weeks. This research collects and analyzes quantitative data, including the pre-test and post-test of teachers' knowledge and perspectives on assessment. The major results generally confirm the effectiveness of P2R-WATA model. Firstly, the assessment knowledge of the participants has improved after training, especially for teachers with low-level prior knowledge. Secondly, the findings also reveal that there is a significant improvement on teachers' assessment perspectives. (Contains 7 tables and 11 figures.)