Her'e a strategy to practice main ideas. I've used it during Guided Reading. One of the nice things about our textbook adoption (not a big textbook user, BTW) is that it came with these leveled readers to use during guided reading. There are all different genres, too, so it actually supports our standards. I was working with a group of fifth grade kids when I did this lesson, but I've used it before with third and fourth graders.
First, of course, we previewed & predicted about the text.
This book is all about changes on Earth caused by different forces: water, weather, and plate movement in the Earth's crust.
In our small group, each child has a book and a post-it. We look at a paragraph at a time. This page was all about Landslides, as you can see by the heading and photograph/caption. I want kids to start using the features to predict what the section will be about, so we have a conversation. Then I have each student read on his/her own, but seated at the table with me.
As they read, they are instructed to find the 3-4 words that the paragraph is mostly about and record them on their post-its.
After each student has recorded his/her words, we talk about which words we chose and why. This is an opportunity for students to revise their words. For example, while we were reading a paragraph that included a list of characteristics of weather, the words hot and cold came up. A couple students wrote "hot" and "cold" on their lists, using up two of their four words.
Another student, however, wrote "temperature." This idea incorporated both hot and cold, as well as several other sentences in the text. Kids can become more evaluative in their choices and really think about determining the most important ideas represented in the text.
After kids get good at identifying the main ideas of paragraphs, we move into sections. Then, they write a main idea statement for each section and combine them to create a summary of their reading.