This research conducted quasi-experiments in four middle schools to evaluate the long-term effects of an intelligent web-based English instruction system, Computer Simulation in Educational Communication (CSIEC), on students' academic attainment. The analysis of regular examination scores and vocabulary test validates the positive impact of CSIEC, and in most cases, the positive impact is statistically significant. The reliability is ensured by the spectrum of the students from Grade 1 to Grade 3 in three junior high schools and from Grade 1 to Grade 2 in one senior high school, and of the teachers with or without blended learning experience, as well as by the various school locations from rural to urban areas in four provinces of China. The learning content-oriented design and the instant feedback feature of the web-based system, as well as its regular integration into the English class, contributed to its reliable positive effect on students' learning performance in ordinary examinations. This is the research's implication for instructional design. The conclusion of this paper could serve as a reference to the technical feasibility and pedagogical benefit of regular usage of appropriate Computer Assisted Learning system in the mainstream subject of middle schools. The multiple quasi-experiments in divergent school settings to ensure the results' reliability distinguish this research from previous ones that just implemented one single experiment in one school.