The purpose of this study was to assess CALL software (AceReader) effectiveness in developing TOEFL reading proficiency of Iranian EFL learners in comparison to paper-based instruction and to investigate any significant difference in the TOEFL reading comprehension of the high and low proficient learners after receiving computer-assisted instruction. The 123 female participants of the study, who were 60 high and 63 low proficient learners, were randomly divided into four groups, two experimental groups and two comparison groups. Sample TOEFL reading comprehension passages were used as the material of the study during the 16 sessions of the instruction. Before the instruction began, the participants in the experimental groups were trained for about two hours in order to be able to use the software effectively. A sample TOEFL test of the reading section as the pretest and posttest was also administered. The findings of the study indicated that there was a significant difference in the TOEFL reading comprehension of the learners who received CAI (Computer-Assisted Instruction) in comparison to those learners who received paper-based instruction. Furthermore, there was a significant difference in the TOEFL reading comprehension of the high and low proficient learners who received CAI.