This study aimed to investigate the effect of Mobile-Assisted Language Learning (MALL) as compared to paper-based instruction in the development of Iranian EFL elementary learners' writing skills. The research purpose was threefold: 1) to investigate the effect of MALL on elementary learners' writing skills; 2) to make a comparison between the obtained results of MALL and pencil-and-paper methods, and 3) to assess elementary students' attitudes about learner involvement in collaborative learning (CL) settings through mobile phone (MPh) interactions. For this purpose, 30 Iranian EFL elementary students were selected and randomly assigned to two groups: one experimental and one control. While the experimental sample received mobile-based instructions on their writing assignments, the students in the placebo group were provided with only paper-based instruction. The findings revealed that the participants in both groups showed considerable improvement on the immediate and delayed writing post-tests; however, on average, those in the experimental MALL group were shown to have outperformed the students in the control group significantly. Not surprisingly, the learners in the treatment group had made fewer errors on the targeted grammatical structures like the use of adjectives, possessives and simple present tense compared to those in the control sample. Finally, the results of the post hoc interview reflected that MALL learners felt positively about the utility of mobile technology in writing classes. Essentially, the findings could be of great help to EFL teachers, EFL learners, and course designers.