This study explored the effectiveness of using assessment rubrics as a learning tool in an English-Medium Instruction (EMI) context at a Japanese university. 88 undergraduate students in three EMI courses participated in the study. Students in Course A (n=30) were second-year students enrolled in an EMI course for the first time, with limited prior experience of assessment rubrics. Students in Course B (n=28) were third-year students, most of whom had been enrolled in other EMI courses where rubrics were used. Students in Course C (n=30) were second- to fourth-year students, and the majority had no previous experience of assessment rubrics. In Course A and Course B, both content-focused courses, for each assignment, rubrics were introduced and reviewed, referring to a good example. Course C, a language-focused course, used assessment rubrics for numerous in-class activities, including self-assessment and peer review. At the end of each course, students answered a questionnaire about their experiences with using rubrics. Overall, students’ responses indicated various positive effects of rubric use. First, rubrics helped students better understand characteristics of good task performance, which allowed them to focus on important aspects of each assignment. Rubrics also helped them better interpret how they did and what area(s) they needed to work on. However, a handful of students in each course confessed that they were not able to make full use of the rubrics on their assignments. Interestingly, the proportion of students who failed to take advantage of rubrics was smallest in Course C. This finding may be because students in Course C had numerous opportunities to work intimately with the assessment rubrics through self-assessment and peer-review, which in turn may have helped them better understand and value the rubrics. Students in Course B were more likely to use the rubrics than students in Course A, perhaps because they had used similar rubrics in previous courses. Another interesting finding was that use of rubrics alone was not enough: students appreciated and valued feedback from the teacher and peers in combination with the rubrics.  To improve effectiveness of instruction, it is necessary to familiarize students with rubrics through hands-on activities, such as peer-review. It is also critical that students get sustained opportunities to work with rubrics; the use of rubrics needs to be introduced at the curriculum level, beyond a single course. Finally, teacher and peer feedback complement the effectiveness of rubrics and help ensure the efficacy of instruction.