Under the constraint of classroom time, English as foreign language (EFL) learners usually do not have adequate opportunity to practice oral English in class nor receive individualized feedback from the instructor. After-class practice constitutes an essential component of foreign language learning. This study investigated the effect of utilizing rubrics on EFL learners' oral English using a 16-week experiment and a questionnaire. A total of 61 college students participated in the study, 41 in the rubric-mediated group and 20 in the control group. They were required to complete six tasks of three types: conversation, description, and discussion. Participants in the rubric-mediated group were provided with three rubrics describing respective task assessment criteria. They were also required to record their speaking, self-assess their performance with reference to the rubrics, revise their speaking if they noticed they did not meet the criteria, and finally complete a questionnaire. Students in the control group were assigned the same tasks but were not given the rubrics. Two oral tests were delivered at the initial and final stages of the study to measure the change in their speaking ability. Results revealed that rubrics had positive effects on discourse length, discourse organization, and linguistic flexibility but little impact on linguistic accuracy. Responses to the questionnaire indicated that students perceive rubrics as a facilitative tool of practice and self-assessment.