the purpose of the present study was to see which one of the two instruction-processing instruction (pi) and meaningful output based instruction (mobi) accompanied with prompt and recast- is more effective on efl learners’ writing accuracy. in order to homogenize the participants in term of language proficiency a preliminary english test (pet) was administrated between 74 intermediate students at takhtejamshid language schools of karaj. sixty participants whose score fell one standard deviation above and below the mean were selected and randomly divided into two equal groups. one group was taught and practiced processing instruction (pi) and the other group received meaningful output-based instruction (mobi) and did not practice processing strategies. before starting any treatment a free-writing was administrated at the first phase of instruction as a pretest. moreover, at the final phase a free writing posttest was administered among the participants in both groups in order to see if there was any significant difference between their writing accuracy. the pretest and posttest required the participants to use three english tenses (simple present, simple past, future) in their writing. the mean scores of both groups on the pretest and posttest were compared through a t-test. the results of the post test revealed that the participants receiving pi had significantly outperformed the mobi group regarding their writing accuracy.