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The current literature on second language pedagogy promotes a return to some form-focused instruction where collaborative tasks are encouraged.  This study reports on the impact of form-focused instruction and peer revision (text-editing collaborative task)on subjects’ final performance in second language writing in two rhetorical modes of narrationand exposition produced by 60 junior and senior students of English divided equally into the controlled and experimental groups. The results confirmed that form-focused instruction has a better impact on simple than complex grammatical elements. The study also confirmed the significant effect of the form-focused instruction on the inter-lingual errors, and it revealed some positive effects of collaborative task especially on more proficient learners. The findings also disclosed that different processes are involved in editing as well as reconstructing expository and narrative genres. The fact that writing narrative texts was more demanding than the exposition for the learners implies the complexity of this genre in terms of cognitive processing and linguistic presentation, hence a more involvement of writing teachers on this genre is recommended.