This article reports the results of a research study to determine the washback effect of an oral assessment system on some areas of the teaching and learning of English as a Foreign Language (EFL). The research combined quantitative and qualitative research methods within a comparative study between an experimental group and a comparison group. Fourteen EFL teachers and 110 college students participated in the study. Data were collected by means of teacher and student surveys, class observations, and external evaluations of students' oral performance. The data were analyzed using descriptive statistics for qualitative information and inferential statistics to compare the mean scores of the two groups by One Way Anova. Results showed positive washback in some of the areas examined. The implications for the classroom are that constant guidance and support over time are essential in order to help teachers use the system appropriately and therefore create positive washback. (Contains 3 tables and 1 note.)