This study, adopting a mixed-methods design, investigated the difference between the effects of immediate and delayed feedback on Iraqi EFL learners' writing performance. Initially, Preliminary English Test (PET) was given to a sample of 300 EFL learners at the pre-intermediate level and 175 whose scores fell within the range of +/-one standard deviation from the mean were selected. Next, these 176 learners were divided into two groups one consisting of 87 and the other comprising 89 learners. Following that, the scores of writings in PET used for homogeneity purposes were used as the writing pretest scores. Next, in one of the groups (N=87), the learners did a writing assignment in the class and the teacher provided them with immediate feedback. In another group (N=89), the learners did a writing assignment each session but were provided with delayed feedback after three sessions. After 10 sessions of treatment in which learners did 10 writing assignments, the writing posttest was administered. Finally, 20 learners (10 from the immediate feedback group and another 10 from the delayed feedback group) were interviewed to explore their perceptions regarding the contributions of immediate and delayed feedback to EFL learners' writing development. Moreover, the 20 teachers who taught the classes were also interviewed. The results of One-way ANCOVA indicated that the participants in the immediate feedback group outperformed their counterparts in the delayed feedback group. Moreover, the results of paired samples t-test showed that both types of feedback were significantly effective on learners' writing performance. The results of qualitative data analysis for learners revealed five themes for the effectiveness of immediate feedback. The five themes included immediate feedback enhances writing performance, motivation and engagement, error identification and correction, overall writing skills development, and real-time improvement. Moreover, the results of qualitative data analysis for learners revealed three themes for the effectiveness of delayed feedback including reflection and long-term development, understanding strengths and weaknesses, and time for improvement. The results of qualitative analysis for teachers' perception of immediate feedback demonstrated six themes consisting of immediate feedback enhances writing performance, motivation and engagement, error identification and correction, real-time improvement, constructive and supportive feedback, and enhanced learning experience. The results of qualitative analysis for teachers' perceptions of delayed feedback unraveled three themes including reflection and long-term development, understanding strengths and weaknesses, and strategic improvement planning. Based on the results, EFL teachers are encouraged to employ immediate feedback more in comparison with delayed feedback to enhance EFL learners' writing performance.
