This study introduces the development of a Web-based assessment system, the Web-based Assessment and Test Analyses (WATA) system, and examines its impacts on teacher education. The WATA system is a follow-on system, which applies the Triple-A Model (assembling, administering, and appraising). Its functions include (1) an engine for teachers to administer and manage testing, (2) an engine for students to apply tests, and (3) an engine for generating test results and analyses for teachers. Two studies were undertaken to assess the usefulness and potential benefits of the WATA system for teacher education. In the first study, 47 in-service teachers were asked to assess the functions of the WATA system. The results indicated that they were satisfied with the Triple-A Model of the WATA system. In the second study, 30 pre-service teachers were required to use the WATA system during the teacher-training program. After 4 months of experience in using the WATA system, the pre-service teachers' perspectives of assessment have been changed significantly. The findings of these two studies might provide some guidance to help those who are interested in the development of Web-based assessment and intend to infuse information technology into teacher education.