One major advantage that classroom teachers have over online teachers is the ability to interact with students directly, and help them correct their own mistakes on writing tasks. Immediately. Directly. Face-to-face. Try to get the students to understand what they are doing wrong for themselves. One way to do this is through the self-correction technique. This is what I usually do in class.
When I return writing tasks (IELTS or general English) to my students, they come with little letters above the words or phrases, codes to tell them what
type of mistake that there making. Is it a missing word?(mw) Is it a lexical, a word choice, error?(wc) Is it a grammar error?(gr) Spelling?(sp) Then, I insist that the students don't just look at it and put it away, that they do their best to correct their own mistakes, and then ask me, "Hey teacher, is this right now?" or, "I'm sorry teacher, I don't understand what I did wrong here. Please help."