This paper aims to examine the effects of level-differentiated-task-based teaching on the development of primary school students` English reading and writing skills. A total of 75 sixth graders (38 students of a control class, 37 students of an experimental class) were participated in the study. They were divided into an advanced group and a remedial group in a class, respectively. Each group of the experimental class was taught for 10 weeks (twice a week) through different reading and writing tasks for this study which were developed to fit for the students` different levels. To find out the results of the study, reading and writing tests, a questionnaire, and self-evaluation were administered at the end. The findings of the study are as follows; 1) level-differentiated teaching had a positive effect on the literacy development of the advanced group while it didn`t influence the learning of the remedial group. 2) level-differentiated teaching contributed a lot to the students` interests and confidence in English in an advanced group but not in a remedial group.