In response to the educational challenges posed by the Covid-19 pandemic, students and teachers have adopted the pedagogical shift of emergency remote teaching (ERT). Vietnamese students began learning online in March 2020 and subsequently switched to offline learning in February 2022. As a result, schools have modified course materials and delivery methods as needed. Students have also shown resilience and adaptability to their learning strategies which are manifested in their learning inputs and outputs. Many ESL teachers have noted a difference in the quality of work produced online compared to in-class impromptu writing. Thus, the researchers would like to compare the students' writing outputs in online and offline classes. The written outputs of 120 students will be analyzed in order to evaluate their grammatical and discourse competence. This research will employ mixed method embedded design using thematic and discourse analysis. While grammatical complexity is measured through Co-Metrix application, the range of student's vocabulary will be assessed using type-token ratios (TTR) using VocabProfile. Meanwhile, the ability of the students to use a range of cohesive devices will be analyzed using Guy Cook's formal and contextual links. Since writing is a complex skill, it is important to understand the students' processing and attitudes towards the writing tasks in two different contexts. Thus, an interview will be conducted and the responses will be coded using NVivo10. The researchers hope that this paper will provide insights to curriculum designers and teachers in planning their writing lessons and projects.