As a current student and a future educator, I have found that not only do students sometimes struggle with figuring out what the main idea is and what their author wants them to take away from their writing. I found this main idea set that has 5 activities for science and social students and also contains many tools such as posters for the teacher to use to explain the concept of man idea. This teacher on TeachersPayTeachers has sets that cover multiple topics within science and social studies, which I enjoy. Click here for the link.
Main Idea Kit