Make sure your students already know the difference between a subject and a predicate. Tell the students a simple sentence is a complete thought. It has only one subject and one predicate.
Write a simple sentence on the dry-erase board. Use a blue marker to write the subject and a green marker for the predicate. All other words and punctuation should be written in black. The color variations will help the students to easily identify the elements of the sentence.
Explain what each color indicates.
Repeat steps one through three a few times, until you feel that the students grasp the concept.
Explain that a compound sentence puts two simple sentences together by adding one comma and one coordinator. Explain that a coordinator is a word that puts the sentences together so that they make sense. Tell the children that the words "for," "and," "nor," "but," "or," "yet" and "so" are all coordinators.
Write a compound sentence on the board using the same color scheme. This time, use the red marker to write the comma and coordinator. Explain to your students what the red color indicates.
Write several more example compound sentences until your students understand the concept.