Summarizing and Note Taking

Hello! I am a reading teacher for struggling 6-8th graders. I have been trying to teach my students to summarize but they are really struggling with the concept. They seem to have trouble deciding which details are important and usually include many that are not needed. I have tried selective hi-lighting but many of them end up hi-lighting almost the whole page. Are there any ideas on how I can help my student determine what to include in a summary? I would like this skill to lead into effective note-taking. Thank You!