Systematic Explicit Teaching: Sentence Structure
If your students are using the Riggs program, they already know that spoken words are the signs of ideas. They also know that written words are symbols for spoken words.
If you have gotten past lesson 36, your students also know that words can be strung together to form sentences, which are the signs of thoughts.
By now your students have begun to write sentences from dictation, and they have begun to write sentences which illustrate their new spelling-vocabulary words.
In fact, by lesson 72 your Riggs students will have written so many sentences (dictated and original) that they will be ready to begin a formal study of syntax.