I feel that society is failing many of our children in the teaching of writing skills. A solid paragraph should start with a topic sentence that tells what the entire paragraph will be about. That topic sentence is then followed by supporting details. The paragraph ends with a concluding sentence. Typically paragraphs are 6-8 sentences, but in high school, some paragraphs tend to be one page typed (double spaced) or longer.
To practice writing skills, I make up questions or find pictures from the Internet, have my students bullet point some notes, arrange the notes in order, and then write a paragraph using vivid, descriptive language. Here are some samples: