Nowadays, language errors are viewed as indicators of learners’ existing knowledge of the target language. Several studies have thus been conducted on the types and sources of these errors in order to help learners effectively acquire language skills. This is not an exception in Thailand where students’ English writing has been reported to be a chronic problem. However, there has been little research on the ways to help Thai students improve their English writing skills. Adopting the combined peer-teacher feedback model developed by Nguyen (2017, 2018) and employing a survey and a focus group semi-structured interview, this study reports on how this feedback model helped reduce Thai university students’ writing errors and how they responded to each error for the improvement of their writing accuracy. In addition to confirming the effectiveness of this feedback model in assisting Thai students, the study also discussed their evaluations of each error difficulty level, their revision strategies and the frequencies of their accurate corrections. The results of this study are therefore expected to shed more light on how to help Thai students overcome their English writing difficulties, reduce their writing errors and improve their writing skills. Furthermore, the study is hoped to partly reflect how in-service teachers tailor teaching approaches and materials to enhance the writing ability of EFL learners