I would like to respond to Greg's post below. I am currently working on a paper regarding a lot of the issues you brought up in your post (in fact, I may refer to your blog post in my paper, if that is okay). I agree with your assessment that when working with ELL students who are fairly proficient in English it is easier to focus on the bigger picture when it comes to their writing, but you asked what about those ELL students who do not have as easy a time with the language.
I think the key to this issue is offering choices and learning to be a good listener. For instance, if you don't understand what someone is writing, just ask questions. Sometimes an ELL student will use a word that doesn't quite make sense to our native ears. If we ask them questions about what they are trying to write/say then we can offer them several choices for a more appropriate word choice. But in order to ask the right questions (or at least questions that will get you from point A to point B, you have to listen carefully to what the student is saying.
I think a lot of us, as native speakers, tend to assume what ELL students are trying to say in their writing (or verbally) and we need to step back and really pay attention to the student and try to uncover their meaning. We can't assume what they are trying to say. Often times, if we ask questions, we can help them discover the language they need to express their meaning. And if they don't have the proper vocabulary, we can offer them choices to find the right words.
I really don't think that working with ELL students is that much different than working with native speakers of English. For the most part, we could take a lot of the suggestions offered for working with ELLs and apply those to our tutoring sessions with native speakers as well. Thanks for providing me with a prompt Greg!