Divide the classroom of third-graders into pairs. Have them work together in pairs to brainstorm topics for a paragraph. Each student should come away with one topic; the topic can be on any subject, from bears, to space, to apples. Ask for volunteers to share their topic ideas with the class, and give assistance to confused or struggling students. Provide the students with a sheet of white or lined paper, along with several pieces of scratch paper, and tell them to write their topic title across the top of the paper.
Instruct the students to re-form the pairs they were placed into previously. Have them talk about the subject each picked with their partner, why they picked what they picked and any interesting facts they might know about their topic. Encourage them to try to remember the most interesting facts they talked about in pairs. Walk throughout the room and help students pull out facts and bits of information; for example, a student talking about bats might want to emphasize that bats can fly. Have each students write down three or four facts about their subjects using basic words and without paying attention to spelling or punctuation.
Write a sample subject of your own on the board: gold, for example. Explain to the students that a paragraph is a collection of sentences that fit together and are about one thing. Further explain that the first sentence of a paragraph, or the topic sentence, tells the reader about a topic very generally, but that the rest of the sentences give more detail about what's mentioned in the topic sentence. Write a sample topic sentence on the board like, "Gold is a yellow metal that many people around the world want." Write several facts about the chosen topic to the sides of the topic sentence, and develop simple sentences about each fact. Finish the demonstration by writing all of the sentences together, with the topic sentence first, into a coherent paragraph.
Shift the classroom over to silence and ask your students to write a topic sentence that talks very generally about the subject, along with one sentence for each fact. Encourage them to take their time thinking of the best facts and writing their sentences accurately. Be available to help students that are falling behind, and spot-check spelling and grammar as you circulate. Have them write their complete, simple paragraphs on a clean sheet of paper. Share exceptionally good paragraphs with the rest of the class.