This study investigates and compares the efficacy of differentiated instruction and traditional-based instruction on enhancing Iranian students’ reading comprehension. Eight elementary, intermediate, and advanced classrooms from 1 language institute were chosen, and based on their performance on the pretests were further divided into 4 control and 4 treatment groups. Flexible grouping, tiered instruction, and tiered assignment strategies were adopted to differentiate the content, process, and product in the treatment groups. Results of the final achievement tests revealed that implementing differentiated instruction was effective in fostering the participants’ reading comprehension in the elementary and intermediate classrooms, but no meaningful difference was found in the final performance of the advanced level classrooms.
