We conducted a comparative study to evaluate the efficacy of synchronous and asynchronous interaction modes when providing feedback for improving academic writing, achievement motivation and critical thinking. The participants undertook an academic writing task, and were given feedback by a mentor using one of three interaction modes: asynchronous, synchronous e-feedback, and face to face. Data was collected from the participants via an assessment rubric applied to their writing after each stage of interaction, along with pretest and posttest questionnaires, and a semi-structured interview at the end. We found that synchronous feedback is more effective in increasing the quality of academic writing and achievement motivation, but for critical thinking we did not find any significant difference. We suggest that a strategy combining the advantages of each mode of interaction, considering the writers' experience, may be the most effective way to promote academic writing, achievement motivation and critical thinking.