When introducing “how to find a main idea” or synthesis of the main idea, I share a framed photo analogy with students. Chances are you have a framed photo in your classroom somewhere, correct? If I asked your students, “What do you notice in this photo?” they could probably identify you and family members and even a location like the beach or Disneyland. They might also notice that the people in the photo are smiling and/or holding hands or standing close to each other. If I continued by asking, “Why would your teacher frame this photo?” They would immediately respond with “Well, that was a special day or a special memory.” This is a main idea of the photo!
You have lots of photos of you or family members, but why did you frame this one in particular? Because in this photo, the details come together in a particular way to convey a particular idea–that this was special person or pet or event or experience. This is how we synthesize a main idea in an informational text. There are lots of details in each informational text and you could probably find some of the same details in other texts. But put together the way they are in this particular text, they convey a particular idea. The details are related, connected to each other and the main idea.
For example, consider Grandma Elephant’s in Charge by Jenkins. There are lots of books about elephants, but in this particular book Jenkins puts common facts together in such a way the reader sees how the matriarch of the family is knowledgeable about such things as where there’s food and when there’s danger. Put together as they are in this book, the main idea becomes clear. It’s the same way with current events articles, with longer books, with essays, etc.
I’ve used this in 2nd-8th grade classrooms! If you use this analogy, then when students go to read to determine the main ideas in a text, encourage them to think about how the details are related or connected (the photo) in a way that conveys a main idea (the frame).
If you need more information about this, I describe the frame analogy and sample lessons in Chapter 3 of my book Close Reading of Informational Texts.
Hope this helps.