Writing is an important communicative language skill. It is an activity that requires a mental effort to "think out" the sentences and the ways of joining them to be meaningful and communicative. The present study was set up to the effectiveness of collaborative instruction on developing EFL students' writing ability and also to delve into their attitudes towards it. For this purpose, 30 EFL students (1825) studying at Gelisim University in Turkey were chosen by quasi-experimental research design with a pre-test, treatment, and post-test design using intact EFL classrooms. The obtained data was analyzed using the T-test. The results of the data analysis indicated that there was a positive and significant impact on the development of learners' academic writing skills. Therefore the importance of writing in international communication and the complexity of this skill necessitate the application of appropriate teaching and learning strategies and approaches.