Main+Idea+and+Supporting+Details

The ability to read something and determine what it was about in a couple of words is an important but occasionally difficult task. Frequently students get distracted by their own initial thoughts about what the paragraph or longer reading was about and neglect to pay attention to the details and their relationship to the actual main idea.

Some research suggests that students that struggle with reading may do so because they draw conclusions very early about what a passage they are reading is about and fail to adapt as they read. The ability to stop during reading and answer the question "What is the main idea?" can be an important step for some students.

A that, while it seems simple, will ensure that students understand the process of deriving the main idea when asked.

Some other resources:
An explanation of main idea for students in text followed by some. I would assume you would be better off using your own texts, but the exercises may be helpful.

Another interesting exercise in helping students grasp the relationship between main idea and supporting details is occasionally asking them which sentence(s) in a paragraph does not contribute to the main idea.

While this is actually about summarizing, it connects the task of summarizing to identifying the main idea and supporting details. I can't stress enough that, as simple as it is, having students do summarizing exercises is easily the most bang for your buck in developing critical thinking in relation to your content and what they have learned.