The importance of input has been a broadly documented concept in the field of second or foreign language acquisition. However, kinds of input and ways of its presentation are among the controversial issues in L2 classroom research. Therefore, this study was designed to compare the effects of three kinds of input-based instruction on intake and acquisition of the English causative structures by Iranian EFL learners. A total of 105 university students in four intact classes were randomly assigned to four different conditions: processing instruction (PI), textual input enhancement (TE), consciousness-raising (C-R), and control (CO). A pretest/posttest (immediate and delayed) design was used, where participants’ ability to interpret and produce the target structure was assessed through administering a multiple choice interpretation test and a sentence-level production test. Moreover, a grammaticality judgment test was run to assess the amount of intake. Results revealed that learners in the PI group significantly outperformed learners in the other groups on both immediate/delayed production posttests. The findings also indicated that, C-R group could not retain the significant effect of instruction on delayed production posttest and TE tasks were not effective in improving the learners’ production of the target structure. Moreover, the PI group outperformed the other groups on grammaticality judgment test too. Based on these findings, we can conclude that PI which encompasses the most outstanding features of both focus on form and meaning instruction might be a more effective approach in helping EFL learners to acquire the target grammatical forms.
