This research analyzed the efficacy of ChatGPT as a tool for the correction and provision of feedback on primary school students' short essays written in both the English and Greek languages. The accuracy and qualitative aspects of ChatGPT-generated corrections and feedback were compared to that of educators. For the essays written in English, it was found that ChatGPT outperformed the educators both in terms of quantity and quality. It detected more mistakes, provided more detailed feedback, its focus was similar to that of educators, its orientation was more balanced, and it was more positive although more academic/formal in terms of style/tone. For the essays written in Greek, ChatGPT did not perform as well as educators did. Although it provided more detailed feedback and detected roughly the same number of mistakes, it incorrectly flagged as mistakes correctly written words and/or phrases. Moreover, compared to educators, it focused less on language mechanics and delivered less balanced feedback in terms of orientation. In terms of style/tone, there were no significant differences. When comparing ChatGPT's performance in English and Greek short essays, it was found that it performed better in the former language in both the quantitative and qualitative parameters that were examined. The implications of the above findings are also discussed.