This article is an action research of quasi-experimental nature. It aims at investigating the effect of CALL-based instruction on Yemeni students' score attainment on the TOEFL iBT. The sample of study consisted of 30 adult students randomly assigned to experimental and control groups. Data was collected within an 8-week period via a pretest-posttest design for equivalent groups. The experimental group participants were also interviewed to elicit data about their attitudes towards CALL. The findings of the study indicated that there was a statistically significant difference between the experimental group (trained with CALL) and the control group (trained conventionally) in the total gain scores, as well as in the section gain scores of reading, listening, speaking and writing. The findings also showed that the participants in the experimental group held positive attitudes towards CALL. Therefore, it is highly recommended that CALL should be fully integrated into TOEFL iBT preparation programmes.