Computer-assisted instruction has some beneficial effects on EFL learning. Via the use of computer,learners can pick up language knowledge or skills more quickly and they can also keep language knowledge or skills for a longer period of time. The present study aimed at examining the effect of computer assisted instruction on learning subject-verb agreement in English grammar, which is one of the problematic areas for EFL learners, especially at the elementary level of language learning. To this end, a sample of Iranian EFL learners was randomly selected and assigned to two groups; experimental and control. The experimental group received the treatment which included Rosettastone software that is based on 'Dynamic Immersion Method', in which second and/or foreign languages are taught in a natural way as they learn their first language. During this period, the control group merely worked on the textbook.