Even though I write for a web site professionally, I wasn't effectively teaching the concept of how to know when to start a new paragraph. Worse yet, after decades of "just knowing" when to start a paragraph, I could not come up with another way to teach this.
I did some research to get help with teaching about paragraphs, and found Purdue's Online Writing Lab's On Paragraphs to be a great resource to help with explaining paragraphs. Homeschool teachers can translate this information to the appropriate grade level for their students, while older students can use it as a refresher when needed. On Paragraphs is printable, and check out the Purdue OWL resources for grades 7-12 for more writing resources and instructional material.