Acquiring sufficient linguistic proficiency to perform competently in academic and professional contexts generally requires substantial study time beyond what most language programs can offer in the classroom. As such, teachers and students alike would benefit considerably from high quality self-access materials promoting independent learning out of class when possible and, thus, allowing greater social interaction in class when necessary. The present study is a follow-up to Lyddon (in press), in which a concept-based approach to grammar instruction was adapted into a series of computerized modules. As the number of participants in the previous study was insufficient for meaningful statistical analyses of the learning outcomes, the current investigation redressed this shortcoming as well as responded to survey suggestions for several key changes to the pedagogical materials, including provision of more numerous training sentences, more highly elaborated feedback on exercises, and an immediate remediation option. As before, the purpose of the present study was to determine the viability of a computer-based conceptual approach to teaching English grammar. In a quasi-experimental pretest-post-test design, 31 Japanese university English learners of English for Science and Engineering completed a series of self-paced, interactive online tutorials aimed at teaching the concept of grammatical voice. Gains were then measured in terms of improvement in post-treatment grammaticality judgments. While the findings showed the modules to be generally effective, they also suggest important differences in learner understanding of the use of animate vs. inanimate subjects. Thus, additional study will be needed to focus on this particular issue. (Contains 2 tables and 2 figures.)