The present study aimed to investigate the use of wiki as an assessment tool to improve EFL students' writing accuracy and motivation. Specifically, the study tried to investigate how using wikis can influence EFL students' accurate corrections of errors and writing motivation while they are responding to teacher feedback. The study adopted the quasi-experimental pre-post-test control group design, and its sample consisted of 60 students selected from a Saudi university. The experimental group

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... tudents received wiki-based writing instruction while the control group students received regular writing instruction. The students in both groups were assigned to write five articles with pre-determined topics about different genres of writing. The experimental group students' writings were posted to their wiki. While writing the articles, students were introduced to use grammar checking. They were invited to correct each other's errors and restate the writing by recommending new words and by the instructors' guidance. The instruments of the study included: a pre-/post-writing skills test, and a motivation questionnaire. The study results revealed statistically significant differences between the students in both the control and the experimental groups on the post-test in favour of the experimental group students. There were also statistically significant differences between the mean scores of the experimental group in the pre-administration and post administration of the writing motivation scale in favour of the postadministration. Additionally, the number of grammatical errors has decreased dramatically during the peer feedback. As for the students' motivation, the results showed that almost all students reacted positively to the amount of learning they have received. The results also revealed that the feedback was conducive to Saudi EFL learners' writing self-reflection and self-confidence. It is concluded that collaborative writing via wiki only encourages students' collaboration and selfreflection but also engages them in knowledge noticing and co-construction.